Good point on UA. Though it only makes a difference when one is posting, and a lot of the witnesses don't post or only post their witness report. And often they don't accept rewards. So while it is redundant to give them bigger UA votes, it doesn't come into play that much percentage wise.
It wouldn't necessarily have to be using the actual UA scores though. It could just use their parameters and then diverge from that however seems most reflective of contribution to the platform.
What I like about it is that it rewards people for having an active followership (people commenting on and upvoting your stuff) not for how much SP they have. I think that gets to the point much more.