Hi there..although I have no idea what Addisons is,I have 3 cats similar ages to yours,mostly indoors,but I take them out for a run in my backyard every day for a while.
Anyway,it is my opinion that cats do need a bit of wet food,mine have about 1 1/2 tbsp each in the morning and at night but good quality dry food is available for them all day and cool water of course.I know if I was a cat,I would certainly like a little variation
Mine don't seem to have a problem with hair-balls,but I do not have a longhaired cat,I am not sure,but I think I read somewhere anti-hair-ball food is not that good for the cats,not as a main food.
I hope your kitten will do better I would give him a little wet food.
Ps.Sorry I missread,I thought you were feeding them a hair-ball food.