User blog comment:Willbachbakal/(Item Concept) Crowd Control/@comment-24795478-20150101132103/@comment-1330314-20150101173417

True, a player with very good reactions could block high-power ults more often, but that supposes a 100% success case, which is highly unlikely even against long-distance Ashe ults. By contrast, QSS offers guaranteed CC removal, so right now it can counter those same ults all the time.

A feature that doesn't get mentioned is that, while spell shields can only block one ability, CC removal can undo every debuff and crowd control effect on the user at once, meaning that you can negate multiple abilities at the same time. You still take damage, but that doesn't stop the item from removing the largest part of a lot of abilities' power.