i'm sure each NPC weapon does different damage even if it's held by a specific joker (example: Heavy FBI SWAT with bronco, it should do the same damage like a bronco cop would do)

also yeah it DOES work with Oldschool enemies, the oldschool enemies just replaces the models of overkill units and below and does small changes to some of the NPCs' arsenals (example: red gensec guards use MP5 just like they did in PDTH, and every white gensec uniform guard uses the chimano)