I was going to make a post similar to this, but I'll try to keep it short and sweet since I'm just reiterating your point.
Quan Chi's defensive options in summoner are often cited as his weakness to prevent him from being top X (1, 3, 5, etc) in the game.
This does not factor in how Quan Chi's offensive can be done to ignore the opponents defensive options, making them equal to Quan Chi himself. Meaning they must block.
However Summoner Quan Chi has the best offense in the game. This turns the match into the best offense in the game (summoner) vs no defensive options but blocking ridiculious mixups (opponent). When the opponent is on offense, it turns into NOT the best offense in the game vs no defensive options but blocking, mostly.
Summoner turns every match into an arms race of offense in which he is the best at.
If he possibly loses a match it'd have to do with some sort of neutral game problem. But his neutral game is strong in many matches due to his powerful zoning, great jump attacks and long range overhead.