so to sum up:
- oda stated that humans who eat human fruits become “more human”. this is why it doesn’t make sense to say “luffy stayed in his hybrid form for years”. He actually didn’t have a hybrid form, just like sengoku (who presumably is an awakened hito hito user).
- mythical zoan fruit apparently give both zoan powers and the ability to control a natural element, like kaido and marco with fire, sengoku with electricity.
- why the rubber powers (and the new capacity of transforming the ground into rubber)? i’d say: unclear. it’s probably because nika himself had rubber powers.
- awakening is the base for gear 5, and seems like luffy reached the full understanding of its fruit, just like doflamingo stated in dressrosa.
- joyboy was presumably the previous holder of the hito hito no mi model: nika. the rubber abilities brought joy because they are actually stupid, as Oda always stated. I like this parallelism between the story and the readers