I cant vouch for their reasons for leaving raid weapons behind. For the others though it doesn't have to be about them being OP or nerfed its more so about does Bungie know how players will use them and do they think their original design choices were correct? I mean, look at Y2 Dragons Breath its a bit more fun to use with the Napalm canister perk, but in all honesty the old variants stats and Solar Grenade effect were much better, arguably that weapon was great before but everyone hated it because they felt it was bad(not to mention Gally invalidated the shit out of Dragons Breath) yet Bungie still went on and changed it.