Lol. Dryad's statement is HER statement before HEART SQUAD learned ultimate magic. I'm not saying that the Dryad HERSELF Learned of Ultimate Magic. I can't even fathom how you got this when I said over and over again that she is the one talking about how they can learn ultimate magic. Asta being useless certainly provides evidence to my argument. As he wouldn't be useless in the battle IF he could destroy the heart.
I'll admit I misread about Asta being able to go black form. But, Nacht's statement does nothing to support your argument.
In the same scan, you provide it shows that there are no other devils of notable power. There is Morris and the Dark Triad in the area. But there is no Megicula or Devil Zenon. This is in 291 long before either of those instances. So you cannot extend this statement to Asta defeating Megicula because she wasn't even around at the time of this statement.
"It's completely incomparable? This is really just proving that you are not reading my comments OR just being very disingenuous. They are very obviously comparable.
"Physically draw closer to mana." What is there to not take literal about this? This sounds like YOUR headcanon.
"By making free use of the Mana Method in the Heart Kingdom, You acquired True Magic That use enormous amount of natural mana." She then explains the importance of true magic (In other words). "In other words, You can use more magic than you actually have. That means there's a chance you'll be able to artificially use Ultimate Magic."
This confirms that it isn't True Magic itself that allows them to use ultimate magic. But it is what True Magic does. Allows them to use large amounts of Nature's Mana. More than they can possess themselves. This is what allows them to use ultimate magic, which is stated by the Dryad to be getting closer to mana. Mereo doesn't have True Magic. But she has Mana Zone.
Mana Zone which
absorbs nature's mana. Now what does Mereo do?
She bathes in the hot lava of Nature's mana in the
grand magic region seen here in 275. This allows her to, "...use more magic than you (she) actually have...". She then
physically draws closer to mana (No matter how much you keep ignoring this statement by Adramalech). The Spade rebel thinks
"It's as if she has become one with mana." Which is similar enough to Adramalech's statement. Because he's saying it's as if, not that she literally has. Via this technique that step-by-step, matches Ultimate magic, and it makes her able to kill Lucifero according to himself, paired with all of the other evidence about UM, it can kill devils.
The devil down on the left has the same head shape and elongated arms as the other mid-rankers. We don't see the added detail because they've been taken out. They're laying on the ground.
Actually, the tentacle devil was struck where the heart could be. I'm not saying that Luck killed the mid-rankers literally on that panel. But Luck wouldn't just leave them behind if they didn't die. They aren't there when the manga returns to the same scene where Luck bodied them. With Luck literally mirroring the same ability typeset as Mereo (More mana than naturally can hold, becoming physically closer to mana) And this makes Mereo able to kill Lucifero, then it means Luck can kill the mid-rankers. Especially when paired with: Gaja thinks to himself that UM can kill Megicula, Dryad implication of UM able to kill mid-rankers and higher.
Let us not remember that the crux of your theory revolves around a single statement from Noelle (despite an anti-statement from arcane Asta being useless) and a vague gesture by Gaja (Which is contradicted by his own thoughts) which was extrapolated into being an entire devised plan. The source material debunks your multitude of claims that only saint or arcane users can kill devils mid-rank or higher. As Mereo does this despite being neither, via using an ability that step-by-step matches the description of ultimate magic, which is also implied by a god that it can kill devils mid and above.
More evidence is that the Spirit Guardians are
tired after their fight. It really wouldn't make sense for them to be that tired against ONLY low-rank devils for what wouldn't be that long of a battle. We know that Zagred is a high-rank. We know that
mid-rank is massively above low-rank, and a logical assumption is that there would be a massive gap between mid-rank and high-rank as well. This is further supported since we know that Supreme-rank are way above high-rank, as even the weakest supreme devils (Lilith and Naamah) Dwarfed the power of Zagred. Also, even the gaps between a single level of the supreme-devils are seemingly high as well. Low-rankings are far weaker than mid-rankers, and those mid-rankers should be far weaker than Zagred. So if these were low-rank devils, the Spirit Guardians should have no issue, even with waves of them approaching. Strong people can struggle with groups, but only when the groups have members with relative power power or a hax. But Loro even brings up that
high stages can defeat entire armies of lesser mages, and then it shows
Zenon no diffing 2 generals (Who were stated to be captain level) and diamond army. Also with
Vetto bodying 50 magic knights at once, while not even at full-power, even with some high-level knights included in the slaughter.
The Spirit Guardians were Stage 0 before the timeskip, would have gotten stronger over 6 months, and then got even more powerful training with Dryad and then Ultimate magic on top of it. The Spirit Guardians (pre-TS) Scale even above some clover captains, if not most .
Valkyrie Armor Noelle being stage 1 and bodying Elf Fana who had
more magic power than captains. This is confirmed when in the anime canon, they say they need to be
above Vice-captain power to be Stage 1 (
Senior 1st class is same rank as Vice-captain). This means pre-TS captain level is stage 1. This means that Spirit Guardians are at least relative to Zagred. The waves of low-rankers shouldn't give any of the Post-TS Guardians trouble, let alone four of them. It makes far more sense that there were plenty of mid-rankers and even some high-rankers.
The Spirit Guardians have nigh-infinite stamina against lesser opponents.