Question : QSS vs Certain Champion Abilities

Right now Quicksilver Sash (QSS) works on champion abilities such as Fiora's Grand Challenge and Fizz's Chum the Waters. My question is, why is QSS able to negate abilities that don't cause direct negative effects on the QSS caster? I can understand Fizz's ult because it slows and causes a damage amplify, however I don't understand it for abilities like Fiora's Grand Challenge that doesn't cause negative effects on the target. Sure Grand Challenge unlocks all 4 Vital locations, but the ult doesn't cause direct harm to the target's stats. Having the ability to 100% negate any form of play isn't something that is healthy for the game. With Fizz QSS detaches his ult, but the ult can still call the shark to pop up and deal damage. With someone like Fiora (yes again her because she is the best example for this) her ult vanishes completely removing it from existence while it is on its 110/90/70 cooldown (without CDR). I understand QSS works against debuffs, but it shouldn't work against anything that doesn't cause a status effect (stun, snare, root, damage amp, etc) or lowers stats (movement slow, attack speed slow, AD/AP reduction, etc) because without either of those things can it really be called a debuff?