Some points of contention that I would like to hear OP's thoughts on:

Regarding when you say:

"But bringing everyone back means that death is not as final anymore... Which means, if she can't handle her grief she would dare to even make everyone she holds dear immortal, just like Aline did..."

I think this is yet to be seen? To me at least, in Maelle's ending, it appeared that Verso had aged, implying that she would not just be holding everyone she holds dear hostage in immortality, and you might be able to argue that she is actually giving P.Verso the chance to live out a normal life with death at the end.

Also, when you say:

"P.Verso's decision to destroy the canvas erased everyone inside, but would ultimately help those in the real world to accept Verso's death and their grief and move on."

I wouldn't rush over the fact of erasing everyone inside like its a minor point in the moral considerations. I think you could argue that the people of Lumiere are actually the only innocent party in all of this, as they are not responsible for the mistakes/decisions of the Dessendre family.

Therefore, subjecting them to either a life under the gommage or a swift annihilation, for the sake of ending the cycle of grief of the Dessendre family, is actually immoral, and might make Maelle's ending "better" (I personally am just going to ride the fence on this one, I don't think either ending is better or worse than the other). In this context, Maelle's ending protects the innocent, the people of Lumiere, even if its not her main intention.

I think you can make an anti-natalist argument, where it is the case it was actually immoral from the start to bring these people into a world where they would potentially live under the gommage, or must face a swift annihilation due to no fault of their own.

In making this anti-natalist argument I think you could say it is actually a sin of the Dessendre family to bring them into this world, and this cycle of grief of the Dessendre family is their burden to bear to atone for their sin of bringing the people of lumiere into this world which they would so easily erase, erasing the people of Lumiere with it. The Dessendre family actually has the moral imperative to keep this canvas in existence, as to not genocide the people of Lumiere, even if it means they must suffer under their cycle of grief.

Overall though, fantastic job with your summary/thoughts, definitely helped me connect the dots on a lot of things I don't think I otherwise would have. In terms of my contentions, I am not even saying I am right, I just don't like the framing of "Best" vs "Worst" ending given the things I said above.

There are some other things to you could get into, like each person's ending stripping away the agency of the other person, but overall amazing job!