23 years keeping parrots, never had feather plucking. I consider plucking more often associated with emotional stress: bored, not enough stimulation, neglected, etc.. It can certainly be the result of physical issues also but I always associate it more with emotional issues. I always make sure mine is entertained and kept busy with lots of time out of cage, one-on-one direct interaction, interesting foods/treats and toys. Plus lots of cardboard to chew!!!
I don't clip wings. Mine can fly if they want. I had a cockatiel (23+ yo RB) who could fly so well he could turn a corner on a dime. lol My grey tends to only use flight if startled, to glide gently to the floor.