It really just is verse-specific. Narrativium doesn't hold the same form of importance as Canon does in HS and so on...
Is it, though? I think you are confusing different levels of use with different kinds of plot. Sure, some characters with plot manipulation can't use it to the same extent as other characters, but the same can be said about every reality-warping type of power (i.e. concept, information, causality, law etc.).
Of course not every work necessarily shares the exact same ideas, the same goes for any other power, but there is a wide-spread view of plot that is close enough to make it an ability. Plot as the metafictional representation of reality is widespread and just as much separate and universal then, say, information as fundamental building blocks of reality.
Umineko's plot manip is clearly about fate. That's litteraly the reason why Witches in general have plot to begin with. Hell, kakeras are litteraly crystalized fates.
And Ichiban's part is kinda the entire plot of the last two acts. Needless to say, we've had enough threads on Ichiban not to relaunch that specific debate.
It's definitely Fate Manipulation, and the verse just litteraly consider it to be "the ability to create fate".
Featherine's case is simple to put in fate terms "Lambdadelta is fated to get killed by something, however said something will be unspecified". It's basically the same as prophecy shit you can rewrite. Fate is one of those words that Ryushiki07 regularly switch with "writing" like how he does for "Creators" and "Writers".
Your idea of what fate is supposed to be is terrible and incredibly NLFish. You don't fate manipulate objects into existence from nothing and fate manipulation doesn't explain how an object without defined properties can actually exist. Fate is about predestination, not manifesting reality-warping like effects.
To get this through you stretch the definition of what fate is supposed to be able to do to ridiculous extents. The fact that you need to stretch fate manipulation so incredibly hard to explain how this stuff works, shows well why integrating the power is a terrible idea.
I'm not saying it only is Fate Manipulation, however it is one of the most common ability shown under "Plot Manipulation".
Yeah, not in my experience. In my experience the most common ability is a kind of reality-warping that manipulates the fundamental aspect of a fictional reality that is its plot.
Which would be an exception here. I'm not knowledgeable enough on the Neverending Story to say anything about him, but he apparently constantly writes everything on loop or something?
He doesn't write the verse on a loop (well, he sometimes does, but not always). Not that that is really relevant. Point is that he doesn't break the 4th wall. It's not like he's the only one either.
Ichiban doesn't really break the fourth wall either. It has a metafictional narrative, but it doesn't break the fourth wall i.e. it never displays awareness regarding its fictionality relative to us readers and TLOI is not considered fictional itself.
It is clear from a reader's standpoint. Just like how you can say that it is clear what the Afterlife is. It is the reality after one's life. However it would be ignoring everything that make all these "in-verse plot" so different from each other, the same way all "in-verse Afterlife" aren't the same.
Our current P&A pages are ridiculously bad (which is something currently planned to be greatly improved), and Fate Manipulation is one of them. I wouldn't say we should use the bad quality of one page to justify another's.
And Fate is way more acknowledged than plot by a verse. The only way you can see it that way is by taking your view as a reader of what a plot is in real life, not how the verse treats "plot" as an in-verse element.
You say in-verse, but you generalize that to a lot of verses where it's in my opinion not remotely true. I know so many verses with incredibly vague explanations on what fate is, yet other verses show or tell what plot manipulation is or does better.
And if a verse rewrites a book it will of course expect the reader to know the implications, since that is a thing people understand the consequences of. Your argument is like saying that verses that don't define fire manipulation.
And you have, in my opinion, delivered no proof at all for plot in the verses being that fundamentally different from what a reader might expect it to be. You have shown that plot manipulation can have various applications, but that doesn't mean that the plot being manipulated in itself is anything different.
And your afterlife and hellfire examples are flawed. They are things without real-life equivalence, unlike plot. Nobody in reality would agree what hellfire or the afterlife are, since they aren't things we have in reality. However, we have plot. If you ask someone what a plot is, they will be able to answer and people can agree on the term. And you can take that common understanding of what plot is and apply it to a metafictional setting. Doing so is justified as a setting that establishes that its reality runs on plot is metafictional.
And you haven't yet addressed the fact that a story can't exist without plot, but can exist without fate. From a metafictional perspective, which we have to take when talking about plot, a story without plot can't happen. At least in theory. In practice some fictions will be that way, in the same way some fictions have universes without concepts, but generally speaking plot can be considered a fundamental component of reality.
I also don't believe you can actually revise Fate Manipulation into something more concrete than it is, as that is against its vague nature in most fiction.
Except the Old Man of Wandering Mountain is just one example which is totally different from many other examples, all different from one another. You can just label it as Creation or something similar to the First Box of "The Empty Box and the Zeroth Maria". Or even as a similar case to Beiloune.
Except Creation would be a complete mislabeling as plot manipulation can also erase and manipulate things. And the old man isn't different from other portrayals at its core. It's just a purer case that doesn't add any of the extra stuff you try to reduce the ability to.
Having one of your ability portrayed through a medium such as writing/painting/whatever or have some meta attached to it isn't enough to make it its own separated power, given how it adds nothing.
If by your reasoning anything that is restricted to creating, manipulating or destroying parts of reality add nothing, then we could delete most powers. Plot Manipulation isn't about just being portrayed through writing. Brunhild Schild can modify things via writing and it clearly isn't plot manipulation. Why? Because it isn't manipulating reality as fictional thing.
What it adds is that plot manipulation manipulates reality in a different way and hence has different interactions with other abilities. If you only look at what it does to the area around you, concept manipulation, information manipulation and other forms of reality warping also all seem to do the exact same thing. Difference is that they achieve the same goal using different methods. All of them can turn a stone into a tree, but they do it by manipulating different aspects of the stone. The only practical difference lies in how they interact with other powers and what the abstract thing they manipulate is. And plot is a different abstract aspect. Plot isn't fate, as fate doesn't define reality. Fate might guide the development of the rock, but it isn't involved in its existence. Plot is. Likewise, plot is concepts, laws, information, causality or other abstract component of reality. It's unique in being the metafictional component. The reality a non-reality.
You litteraly have mere comparisons (Instant Death), non-metafictional cases despite being all about being metafictional, and actual metafiction. There's no ground as to what truly defines "Plot Manipulation".
Well, mere examples should possibly not be plot manipulation. Don't blame bad CRTs on the power itself. Non-metafictional cases as such don't exist. Plot is always metafictional, just that it sometimes involves higher planes and sometimes not. The common ground between all plot manipulation is that it is manipulation of a reality as something fictional. It is not unlike applying Dream Manipulation to reality, just like Information Manip (Type 2) could be described as applying Data Manipulaton to reality.
Overall, having something like Plot Manipulation opens the door to re-allowing Hellfire Manipulation, Logic Manipulation (since every fiction has a logic, same way "every fiction has a plot") or the "Afterlife Manipulation" example I've been giving.
All these instances are not related, work on a mechanism that is specific to their verse and has its own inner rules (except when it's litteraly just a comparison, which might be half of the time we label something Plot Manip).
So I stand by my point: Plot Manipulation being a page we created is a mistake in the first place.
I'm actually theoretically much in favour of allowing logic manipulation. I would have created it long ago when I created mathematics manipulation, but as far as I know, barely anyone has actual manipulation of logic as opposed to mathematics or laws. (unless you count not necessarily logic-based paradoxes, maybe) It just didn't have enough users.
I mean, logic is the set of deductive reasoning. It's the power that allows you to make other things transdual, which no other ability does. It enables invoking all kinds of paradoxes, like doing the impossible...
Anyways, that probably isn't the point here. As I said above, I think plot manipulation deals with manipulating a common and separate part of reality. While its effects aren't unique (no abilities effects are truly unique. They could all be emulated by another ability) it has some characteristic applications, such as the creation of objects that hardly make sense in a non-metafictonal sense. Like the mentioned tape that lasts for exactly three rooms, regardless of how much is used, or the object that has no properties as the plot doesn't describe it. Ichiban has something similar with Akuto creating a liquid that is no particular fluid until it is clarified what it is supposed to be. Sure not every character with the ability has these applications. Just like there is no common use for concept manip between all users other than 'can to some degree manipulate concepts'.
And let me say it straight: If you think you resist a plot manipulator rewriting the plot to have you spontaneously melt by a resistance to high temperatures or a resistance to fate manipulation, you're wrong. No basic resistance to those things should remotely cover that.
