I personally do not have individual chickens. I have a flock that has changeable members. I make these decisions based on the peace of the flock, not specifically for one member.
I see nothing wrong with your plan to isolate him for a few months before you make your final decision. What you described as far as what is going in does not fit my preconceived notions, maybe it is just his immaturity. Isolating him might or might not work. Good luck.
