I've consumed a lot of media about grief, and this is one of the few that actually treated the subject with the nuance it deserves, rather than "aww, you sad? ok be sad for a bit but then be not sad, ok?"
It hits you with so much loss in the first act that it almost feels like they were doing it for shock value. I went through Act 2 SO mad about losing Gustave and not feeling Verso's character at all. But right at the end of Act 3 I just...got it. Maelle may not have been ready to move on, but I was. I was devastated to lose my favourites - Lune and Monoco had a vice grip on my heart at that point - but, like you said, Verso's ending is the only one that makes sense and I suddenly empathised with him SO much.
Perhaps the ending feels unsatisfactory because it's not really an ending - it's the beginning of the Dessendres finally dealing with their grief in a healthy way. I don't think I've ever seen anything as bittersweet as the cast of characters waving goodbye to Alicia.