I think Rondo gives up when he's outclassed at point guard. This is not backed up by research, and is purely anecdotal, but it seems like he stops trying if the other point guard is doing well, and keeps going hard when the other pg stinks. It's almost like if the opposing PG lights it up, he thinks people won't notice the discrepancy if Rondo just defers more. But if he's clearly going all out, just like the opposition is, and he's just outplayed by a little bit, it will be more obvious he is outplayed, so he just drifts by instead.