We're all diving into the same pool for the rings, and there's no mention at all of the course being divided up into separate tracks for each contestant before that point.  I agree that it would work better as a competition if there were separate tracks, but its not exactly unreasonable that that thought didn't occur to me and I interpreted Zaer's description otherwise as a result.  As for canceling spells, that does take a move action, meaning he'd have to slow down a bit to do it.  Anyone directly behind him would still arguably be able to make it.