Please note that none of the forests that you deleted is "one big multipolygon with the boundaries as children". They only used some ways that are boundaries as their outers, and that's when its outer is also the boundary. I'm not the only one who map this way. Mappers in other countries also do the same thing, like this one https://www.openstreetmap.org/way/922405753#map=13/4.9162/102.5063.

If you want to map the forest independently, that's totally fine and I'm not gonna stop you... BUT... I would suggest that you do it the moment you deleted the "glued" forest. Otherwise I'm going to revert that deletion. Last time you deleted all of the mangrove forest areas of Mui Ca Mau but only remapped a few of them and then leave it as it was for months. That's the most terrible thing to do.