Ofc he would, might makes right is a mentality, not strict guidelines. They aren't all Klingons. Being best assassin doesn't give you right to kill the local boss.
In John's case, he would not back down when ordered by higher up. He was a powerful mad dog. So the best course of action is to defang him.
None of the other characters had to discover their power as late as John did. And none of those that did, had such a potent one.
John isn't that different from say Blyke.
Isolate Blyke, beat him consistently every day for years, berate him for being weak. Then give him a huge power boost, reward him for being violent, and you would see a lot of bloodshed.
Explanation: Blyke is a person that is fast to anger, and society suppressing him and rewarding him for violence is recipe for disaster. He would try to never be in position of weakness, i.e. trample everyone, and since violence is rewarded he would prefer it.
Growing in ****ty condition, becoming ****ty is the expected outcome.