I'm glad you're seeing some improvement after installing the peepers on the problem hens. I can sympathize as I've been through what you're dealing with. You might read my thread if you haven't already.
https://www.backyardchickens.com/t/697052/i-think-i-found-a-miracle-cure-for-feather-picking
I tried everything, and was quite at my wits end. Even peepers had quit working. Some friends were talking about this feed supplement that had solved behavior problems in their dogs, and I thought, why not try it on chickens? Well, it took seven weeks, but the transformation in the trouble makers was astounding.
In short, I strongly suspect that a lot of the behavior problems we see in our flocks may be caused by poorly absorbed nutrients. Indeed, not only did my biggest problem hen stop her destructive behavior, but at 25 weeks of age, she has actually grown larger! She's happy and calm and doesn't pick on the others anymore. I've been able to remove the peepers from the other trouble makers, too. The only conflicts I see now are just the benign pecking order stuff.
This supplement takes a month and a half before you'll see results, but it's sure been worth it for me.