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Putting O'Neill in CF is a good way to get him injured, and he looks a little faster than he is because he does everything at 100% (and it's weird to see a thick dude in baseball moving fast - this ain't football). I would compare him more to the lite version of Bryce Harper: former catcher who's so athletic he can play the OF just fine and who can steal bases in a pinch too.
But O'Neill won't be a liability on defense, especially once he gets more instruction on routes to balls and better placement vs. hitters. And his ball-tracking skills can't be worse than Aoki's, who (as someone else said) has the route efficiency of a house fly.