"I'll become a murdering supervillain who supplies swindled Kryptonite, Amazos and other stuff to from other bad guys".
Fixed that for ya.
Never liked Johns' take on him either, so I'm not going to bother defending his characterization. But I won't deny that Jason has rage issues. However, bottomline is that he waited, picked the right moment to sneak into the Titans Tower, successfully knocked out some real powerhouses and then bested Tim in a no-holds-barred duel without killing him, after which he acknowledged that the kid was still upto the job.
Hate on his approaches and values, not his competency and intelligence.