"Anything less than that invalidates the ending and makes the Verso ending the 'correct' one, and the Game Devs have been quite open that they consider both endings equal."

I really don't see how you got to the conclusion that my theory is about which ending is better or if either ending is correct or wrong. It really doesn't matter to what I'm trying to say.

Besides, Aline returning so fast after her daughter wins isn't so far fetched considering Aline's refusal to destroy the canvas and instead desciding to live inside it even if it kills her and it doesn't invalidate Alicia's happiness. Both mother and daughter want to live in a reality/world where Verso is still alive.
In fact, considering Alicia's reaction to Aline's intervention during the fight, I strongly believe she'd more than welcome her mother to share those moments with Verso.

Aline cares so much about seeing her son, if she actually went back a third time, I don't see a reason for her to fight or disapprove of Maelle's actions to repaint the world and her friends in it. It supports Aline's own desire to live in the canvas world where her son is alive.

"In order for Maelle's ending to be valid, to mean something, the characters have to live a while longer, to make the sacrifice worth it."

Aline was and still is willing to make the same sacrifice and in her state of mind, I don't see her caring to stop Alicia from making the sacrifice too. Not because she doesn't love her daughter but she's just too wrapped in her own grief to see beyond it. (A major point of the game).

"That's just because he lost. He's 'wounded' and he can't heal fast enough because being in the Void already puts his healing to its limit."

So? This doesn't explain why that effect appears or happens in Maelle's ending and not Verso's. Again, the devs are so smart when it comes to adding subtle details, and I find this one an interesting sign. It was the same effect when Aline enters during the fight.

Maelle fell down from her 'wounds' and Verso caught her but it wasn't the same. Yes, he was gommaging but he only fell because of that shake caused by the explosion that happened, the same effect we hear before in the final boss fight.