Well, Jon would be a handful if he became evil, and he kinda does for a time... maybe not evil but turns to chaotic vigilantism for a while before the BioHazard team is officially formed. He goes bad after spiraling into a depression after his friends are put in danger for what he believes is his fault.
He is an excellent tactician and a great thinker, not only that, he is always open to receive and apply knowledge. The first thing he did after understanding what it meant to possess pyrokinesis was to order Physics books and enroll in fire-safety classes at local firehouses. That speaks volumes of his character, he is an action-taker, definitely not passive. Not only that but he is also a physically active person, so his physique is optimal for a person his age. And I haven't even taken into consideration that he is the vessel to one of the forces of the Universe (yup, he is a handful, alright)
After saying all that I realize how difficult he would be to deal with as a villain... but then again, his moral and justice compasses are too fine-tuned to make him go fully evil... unless outside forces turn him evil, there are two sides to every coin, after all.
BioHazard