I found horsenalities helpful when training my horse. She's a super right bran extrovert. I just thought she was crazy. I'd never ridden a horse who was so driven by wanting to feel safe.
This desire to be secure led her to being extremely buddy sour, insecure in new places, and very "claustrophobic." If I held her back, she came unglued.
I was told by a Parelli person at a playday I attended to give her what she wanted until she didn't want it anymore. I was told when my horse didn't want to stand still/acted like a nut, never hold her back or punish her. Frustration = aggression. Anger = game over. Right brain extroverts want to feel safe with you. They can't if they think you want to eat them.
So I was instructed to circle tightly, faster than she wanted to, until she wanted to stop, and then some. It worked miracles!
After two years together, she's starting to find security with me. She's a very kind, affectionate, hard working horse. She's also nervous, reactive, and fearful, but that's getting better as she gains confidence. I have just to be patient, never get frustrated, and give a lot of reassurance.
But most often that is not the case.
True, there are some horses that are just testing your leadership, but the trick is to be able to tell the difference between a truly dominant horse and one that is just unconfident.
If you can give the horse what he needs, when he needs it, your bond will only be better, the horse will look to you more and you will show yourself as a true leader and not a bossy dictator in what is supposed to be a relationship.