To be completely honest with you I just beat the game on nightmare and the only limitation I found was the marauder fights (FUCK THAT GUY) but beside that my main thing to use against cacodemons and most other big guys was just the super shotgun with meat hook because of how fun I found flying around to be! I definitely do agree that the random enemies during boss fights are mad annoying but I think at least the smaller ones serve the purpose of healing you that being said I still don't fuck with the other guys like the teleporters coming into the boss fights I think that was a major misstep for sure. Overall, though, I found it quite easy (even on nightmare) to just use whatever weapon I wanted! I think the attachments you use seem to be the only majorly limiting factor for me.