Well if the vet says he’s good I would put much of my trust in that. I’m not a vet but I’ve had many cats over my lifetime and I don’t think it sounds serious. Cats loose their coats when a new season comes around so it could be caused by that depending on where you live, weather conditions, etc…
It’s not very common but I have seen one particular Bengal about 4 years back that had a terrible coat of fur. It could just be a genetic hiccup and if that’s the case you can’t do much about it.
As for the food talk to your vet before giving or adding any vitamins or supplements to his everyday food.
I hope this helps
Good luck and best regards