Tho if you really want to, remember that Roach himself disagreed with 5D Player long ago.
That's fine. It just means I disagree with him, too.
Anyway: The first set of counterpoints doesn't make much sense, truth be told. References to the medium through which a fictional story is conveyed don't really invalidate a reality-fiction difference, or else those would not really exist, to begin with. If a character sees a whole universe as part of a story told in a book, we wouldn't reason that they're finitely larger than said universe because they perceive it as a bunch of letters (Made of ink, or graphite).
And I think this becomes a bit clearer when you consider the actual status of the Player: If they existed on the same level of existence as the gameworld itself, with the latter just being very small compared to themselves, then they would be a 4-dimensional creature outright, from all perspectives including their own, and I don't think this has much evidence of being the case. Given what they are meant to be, we can assert that The Player, from their own point of view, is a normal, 3-D person, something that cannot happen if they exist on the same level of existence as a 4-D object (The gameworld) and is conventionally larger than it.
They should be Low 1-C as well, then.
Chara absolutely does scale to the Player as they could reach them and take their Soul. Counting how much of a deal the power of the Soul is, this basically implies that Chara has a comparable status with the Player. Low 1-C Player implies Low 1-C Chara, aka that Chara can transcend themselves, which is nonsense.
Chara can only take the Player's SOUL with the latter's consent, otherwise, as far as we can ascertain, they can't do much to them. This is only further substantiated by how Chara goes ahead and destroys reality regardless of whether or not you agree to it (And even mocks you for thinking you were in control), while, in regards to recreating it, they just sit back if you refuse to give them your SOUL.
Although this still would, of course, mean Chara's Soul Manipulation is Low 1-C to an extent. Just a really shitty one, since they couldn't affect a Low 1-C entity without their consent, but, still a thing. I don't see an issue with that, though. It's not exactly unfeasible for a character to have abilities a tier above their own level of existence.
Neutral on the Deltarune stuff.