Every better available option was still in AAA because there were continuing their progression so that they would reap more rewards at a cheaper salary at the ML level for longer. It is how to play the game smartly and maximize your returns. Not tanking. I would not eat salary cap money by releasing or moving players under contract at the ML level just to get a better product on the field, a better product that was still getting better.
What you're failing to understand (presumably because you haven't played this game for all that long) is that players do progress after they're promoted to the majors. And some of them begin to regress after age 27, so they'll end up (on balance) no better than they were while toiling away in AAA at age 25 or 26. You're also overlooking the reality that players don't typically achieve their peak projections at the same time. For example, a player may hit his projected splits after his power begins to wane, and his glove and arm accuracy might peak after his range and arm strength have diminished.
So you should probably just play the best players at the ML level and see what happens if you make it to the playoffs. You can save a year of service time by holding players back for 25 games, which pretty much everyone agrees is good strategy.