Major spoilers obviously
As a general concept, the story is fine. The father and mother dealt with grief of losing two children and one scarred, and they turn to painting to cope and re-experience those memories by creating them in this fictional world. The mother becomes absorbed in the painting at the expense of the real world, Renoir wants to stop the madness before both she and Alicia (real-world variant) are consumed and lost in the real world too. Verso wants to sacrifice himself to save his sister because that's why he died in the first place, he recognizes this world as fake. Maelle wants to save the painted world, because even though it's fake, there are real emotions and connections here that she feels much stronger than the real world, and she doesn't want all that to go to waste.
The issue is when you start going deeper into the specifics and you realize everything is just handwaved bullshit
Like why didn't the paintress make any attempt to communicate with the people of Lumiere through the Monolith text that she isn't their enemy and that real Renoir is the one responsible for the gommage, and she is just reducing the damage he can do? You would think with 67 years of expeditions sent to destroy her due to a misunderstanding that she would try to communicate with them in some way? Especially considering Maelle (who is much weaker) literally paints her own message on the Monolith during the camp scene.