I don't really care about the existence of belts, they not having a tangible graphic model makes kind of pointless to me at least. I'd rather have their budget stats being spread across the accessories.
As for the soulcrystals, I don't really mind their existence as an item slot, to me it seems just like decoration, because you don't really interact with it, or have bag space issues or anything like that. I'm not particulary fond of the lore behind the soulcrystals, tho, only because it makes most of them kind of a 'snowflake' situation when it comes to roleplaying, but hey, the whole WoL narrative also plays a big role there too.