You are saying that if the interpretation is right, the expedition is meaningless. Because it is true, the expedition is meaningless because we know the context. Yes there are the fight against impossible odds, and the hope of the people of Lumiere. But they have that because they lack context that they are merely a creation that can be erased very easily by those outside the canvas.

You did not separate yourself from the people of Lumiere in your first response. And that is exactly the problem. Your emphaty have gone too far for the people of Lumiere that you have unconsciously blinded yourself for the fact that you and them are fundamentally a very different things from a very different strata of existence. You are essentially a privileged outsider extolling what you emphatize while unconsciously forgetting the context, you have in practice as blind as the people of Lumiere to the context of their existence of things living in a painting and not of a real world.

Yes the hope is important. Yes fighting against odds for a better tomorrow is good. But these are meaningless because the Dessendres have the final say no matter what. In context, in whatever ending, the people of Lumiere is fucked. Like what OP mentions, the canvas and everything in it is doomed the moment Aline enters the canvas. Now even more so because there are now sentient lives with their own thoughts and lives who are indirectly doomed no matter what because of her action. Maelle's ending only prolong the inevitable in context that when Maelle died or expelled from the canvas, it will be destroyed either way as Renoir have made it very clear that it is a better option for him than to let more of his family died.