Top prospects don't necessarily equal higher level of competition at that time though, just that they have higher ceiling. AA isn't solely composed of top prospects, nor are "AAAA" players all complete scrubs. They just may not have enough to make the leap. They were better than AA players, or they would be demoted to AA and let someone else take their spot,
If AAA is the top prospects who are there for half a year to a year, plus everyone who already advanced from AA but isn't good enough to stick in MLB, then by my reckoning this is clearly superior competition to AA. I'm confident that if the Sounds and Shuckers switched leagues for a week, the AAA players would outperform the AA players.