Or the enemy could 5 man push.
Numbers trump raw power for the most part. A tower provides a significant source of defense. Thus, if you are only somewhat ahead, then fighting a 4v4 around the enemy tower is risky. Fighting a 5v4 around the enemy tower is not. You can very easily push them off and take their tower. If you go 1 for 1 in towers, who cares? Just take the next one immediately.
Besides, the above is very unlikely because:
- 5 people push faster than 1 person no matter how fed they are.
- The creeps themselves will make it harder for the one person to push due to the buff.
This pretty much force the losing team to take a risky play, and if/when it fails, the game is pretty much over. That's fun to watch, fun to play, and we can move on because the creep difference prevents people from stalling indefinitely.
The worst thing about DotA is that the losing team has to play risky in order to come back, but doing so doesn't really do anything noticeable. The game still takes forever to end even if you are really fed. While not as bad in League, we still get those kind of things when the comp has really good waveclear and doesn't even let the creep damage chip the tower.
As long as the coup de grace moment doesn't come too early, it should really help the pacing of the game where it's not slowing to a crawl while still letting back and forth games occur.