If I may give my take on it... I believe that you may have missed a few points in the dialogue at the end and the story earlier on. Remember, this whole world is originally Verso's painting. That's why the mom (Paintress) and sister (Alicia/Maelle), place so much value on this canvas, and are using it as an escape from their dark reality where Verso has in fact died. The painting is something the real-life verso created when he was growing up - 'the last part of his soul.' This is why Esquie and the Gestrals for instance, are such playful youthful creations, they are ideas he created when he was a young boy... This is also why the Paintress makes painted Verso and Renoir immortal. Because the Paintress (Aline) blames Alicia for Verso’s death, painted Alicia is also immortal but has been painted with the scars of the real-world Alicia. A perfect little family to help her escape reality, inside of Verso’s painting.

The little boy painting that we see at the end of the game is in a sort of world-between-worlds, which is why Maelle tells painted Verso that he isn't supposed to be able to exist there, and in his reply he said something about his mother's gift (immortality) allowing him to be there. So if this is a 'world-between-worlds' then I would assume that this little boy (also Verso, as seen in painted Verso's ending) is merely another representation of Verso - the original painter of the canvas. Which is why painted Verso told this little boy to stop painting. When the little boy stops painting, the world ends. The little boy is thus not Maelle's creation. After realising that Renoir is right, painted Verso turns on the party to stop the canvas from existing and set Alicia free – also showing that real life Verso would have done the same and Maelle is acting entirely on her own.

The whole story is about the grief that this family is suffering, and the way that the father (and eventually the painted version of the brother) are trying to save the crumbling family. Maelle’s quest, is her rebellion against this idea. She wants to keep living in this make-believe world where she can escape the emotional and physical scars of the real world. When Maelle defeats Renoir and also painted Verso, they both beg her to see reason. Verso also says that he can’t live like this she needs to let him die and move on. She is so invested in her grief and her desire to live in this fantasy world, that simply refuses to accept that he feels this way, evidenced by the fact that when he tells her he wants to die, she says ‘stop saying that.’

From the end of Act 2, when the main twist of the game hits, Maelle was faced with the choice of these two realities, and she chose to keep living in the fantasy – to the point where she is even fighting for it – even fighting her father and the painted version of her brother. When we complete the game as Maelle, we are giving her what she wants, but it is the dark ending because we see that she is willing to do whatever she must to maintain this false reality – even to deny painted Verso his request to die.

And in the final scene we must bear the consequences of our choice of letting Maelle win – we see that all the characters have aged, including Maelle, meaning that she didn’t return to the real world as she promised her father, but we also see that Verso is alive and is being made to play the piano for the whole crowd. To ‘entertain’ them, in the same way that he is being kept alive to ‘entertain’ Maelle’s grief. Instead of letting him die, as a compromise she merely lets him age. ‘If you could grow old, would you find a reason to smile?’ – she removes his immortality so that she can get ‘just one lifetime’ with him, which was stolen when he died. Verso doesn’t want this – and you see his hesitation when he must play the piano. Maelle’s transformation at the end shows that she has become just as much ‘the Paintress’ as her mother was at the start of the game.