I don't think that there is any question that Rak has more raw athletic ability than Keita [who is a pretty good athlete in his own right, especially in terms of his ability to run the floor]. However, Rak is still learning how to harness his physical tools--he's pretty unrefined in terms of basketball skill / instincts at this stage of his developmental curve.
He's also relatively inexperienced. Guy barely played last season, and is playing semi-inconsistent minutes now. It's pretty clear that JB doesn't fully trust him right now, which is why he finds himself benched often at crunch time. That doesn't have anything to do with his long term potential, luckily.
To me, despite having NBA level athleticism, Rak seems like a four-year player. I have a feeling that he could be a pretty darn good player as an upperclassman--maybe something similar to Yancy Gates in terms of how his career unfolds, productivity wise. I just don't think that he's going to put it all together this season like some are hoping.