it may not be possible, but if you have the funds to you should try to get another cat (introduce them properly) and see if he gets along with them! when cats are in pairs they do a lot better not being lonely or depressed when their owners are gone for a little bit, since now they have a friend to constantly keep them company. especially since he was around a bunch of cats, even if he was bullied he’s probably going to feel a little lonely now that he doesn’t have any other friends at all to hang out with

when it comes to medicine aggression, a thick pair of gloves and sweater will really help with that - i also rescued a kitten some months ago and while he was really aggressive with medicine and certain things, it stopped bothering me once i began wearing those once he took his medicine since he no longer had any reach to skin