I completely agree that one-button takedowns are lame. But to me, the ease with which I can dispose of guards is completely irrelevant. If I'm fighting anyone, I've already failed. Whether or not the fight takes 5 seconds or 5 minutes doesn't matter because I'm already reloading my last save so I can avoid combat entirely.
But yeah, needing to get close to guards and aim your blackjack is definitely more satisfying than "Press A to takedown."