Looks like KO is a significantly better rebounder and passer, and also has a legitimate 3 point shot. Also KO has much better ORTG / DRTG compared to Yi's horrible 98/112.
Yi is a .333 career three-point shooter. Also, I haven't found the BBRef ORTG/DRTG to be any useful, but that's just me.
In any case, all I wanted to point out is that having a handful of big scoring games doesn't really mean much -- especially on a god-awful team.
Looking at least at his rookie year numbers, he averaged 1 3 point attempt every other game, and he hit less than 30% of them.
You're right, though, plenty of rookies who have nice scoring nights playing for bad teams never amount to anything.
Still, at least for me, KO passes the eye test as a guy who has the size and skills to become a pretty useful player. That doesn't mean he's guaranteed to get there.
Also -- just because a guy (like Yi, or Morrison) didn't end up sticking around in the league doesn't mean he never had the skills or physical attributes to do it. Each guy, I think, had the potential to become a useful role player, albeit a fairly limited one. Neither guy realized that potential, for whatever reason.