One could argue your "idea" is a poorer version.
From the surface, this just speaks to wanting more loot per dungeon run as if that would "solve" the issue of M+. Basically going to a baseline of 3 item drops from 2 but as I previously mentioned there is a system for providing more loot drops at the higher end.
Second, this idea that you need to "overperform" to get more loot would just INCREASE negative behavior. More players will want to quit the key because hey we're not moving at MDI levels of speed to "overperform".
Sure you might not get your key "depleted" but now you get to play the game of restarting keys. It will be just as frustrating and then you'll complain that players shouldn't be able to leave a M+ key unless the timer runs out or some other requirement.