Yep...I think what you may be seeing is just the molting of their baby feathers and the growing in of their mature plumage. My yard looks like confetti right now and even the younger birds (almost 4 mo. ) are losing their fine, fluffy feathers. That you saw him pull a feather doesn't mean he is picking and eating feathers for protein needs. You free range them in addition to the feed rations and your protein isn't too low...at least, not low enough to cause a bird to pick feathers to eat.
You have plenty of space, so space isn't an issue. A cockerel isn't a production bird, so he doesn't need extra proteins for making eggs. My conclusion is that your birds are doing a soft molt and you witnessed one bird preening another. I see my ol' gals reach over and pull a loose feather on another and my old Toby lost both of his last cock feathers yesterday when I had give them an experimental tug just the night before and they were still pretty anchored...don't know if he pulled them or if someone else did, but those feathers weren't gonna come out on their own any time soon.
I'd release him from jail and just keep an eye on them...could be nothing and just a molting/preening socialization. I wouldn't increase the proteins just yet...just watch and wait. See what develops. The problem with things like this is no one waits to see if it's a real problem or a perceived problem, so they throw down some cat food and pronounce that the cat food did the trick because they haven't seen anymore feather pulling or eating. That's a form of inductive reasoning, but when dealing with chickens and trying to ascertain their needs when they cannot tell us, one has to use deductive reasoning.
That's my best advice!