As I said before, how is Altair going to win if she can't affect Medea's true form and Medea uses Infinity Destroyer or teleports away the second she feels even minimally threatened at all?
Incap is a thing and Altair has a 2-B, Possibly 2-A range even with Teleportation. Heck even if Medea sees her and Teleports to the farthest location from the battlefield on a 2-A scale, her perception of Altair would now extend to that Universe Medea is in and allow her to arrive there.
Once again. They cannot think of or create her if she is erased allthroughout time in their universe. We know for a fact that these thoughts, ideas, and stories of alternate altairs are indeed parallel versions of her in other worlds. I mean, in those screenshots Altair flat out states My existence is sustained by the infinite number of creators who add to this poem. I'll leave out the fact that there aren't actually an infinite amount of creators, and focus on the what she says afterwards. She is sustained by the story of Altair constantly being added to and changed. As I said before, even though the main version of Altair has no background to erase or affect, that isn't the case for the alternate altair's created who sustain her existence
1) Let elaborate again, Altair has NO PAST for NOT HAVING ANY BACKGROUND STORY OR BEING BORN OF A UNIVERSE. This forms her Type 1 Acausality. Additionally, she has Type 4 for Transcending the Causality system that binds the story worlds in the Multiverse. So Medea isn't killing anything in the past to begin with.
2) Altair has no Alternate Versions. She IS the collective idea and creation of all the fanfics and Fanarts and fanvideos. This is one of the reasons why she exists as an Abstraction. Burden of proof falls on you to show that she has Alternate Versions because it was never implied that she has Alternate Versions. Her Abstraction in Low 2-C form is because how all those Universes created by her and Setsuna view her as they are Gods to them.
I'm fairly certain of Medea using her powers before Altair because despite what her profile says in her weakness section, she's actually a fairly careful person who would immediately use her stongest attack on an infinitely weaker opponent just because she couldn't one-shot them casually, or teleport away just because her opponent landed a single successful attack. This combined with the fact that Medea can sense Altair's power and Altair would start off fighting a weaker fragment could spell Altair's end. I mean, even when she was nerfed by Naofumi's infinity zero and Raphtalia's infinity bunker, her EE was still 2-A. Then we have to consider that even disregarding 2-A stuff Medea has a pretty big AP advantage. Even after fusing most of the eight worlds together she couldn't even manifest her true form within them without busting them via her presence alone. Then there's the question of Altair needing weapons for certain abilities...which we can talk about after everything else.
1) I can say the same about Altair instantly info rewriting Medea at the beginning of the match or even possess her or Probability Manip her or Powernull via Law Manip. All of which are Thought Based and In Character for her.
2) Altair can too sense Medea's power. The Extrasensory Perceptions and Enhanced Senses aren't for decorations on her wall you know.
3) It's Low 2-C versions that's being used her and Altair is At Least Low 2-C for creating an Infinite Universes for an undefined period of time. So don't see how Medea has an AP advantage here.
4) Altair doesn't really needs weapons when she's super serious or in trouble and EOS she creates a Universe with it's own Laws and Reality for Setsuna with nothing after saving her.
So your entire argument boils down to Infinity Destroyer which is just Existence Erasure. Which like I said before, is cool and all, but not enough to put her down as Altair has several ways to get through it assuming if she even let Medea use Infinity Destroyer. Whereas Altair has loads of options to incap Medea with that Type 9 isn't gonna help with. The only thing Medea's attack is going to be erasing is the physical image of Altair.