Fioras identity was also Blade Waltz. Where is it now? huh? oh right... You can argue the new Fiora is better than the old one, but you cannot argue Fiora lost her signature move.
Her "I may die 7 times straight but so will be your adc once teamfights start" mechanic is gone.
Olaf used to be an unstoppable unkitable Tank Damage Dealing machine that ran at you and zoned 3 or 4 members of your team for 6 seconds just by being there. It was pretty retarded when he was strong but it was his identity.
Sions identity used to be his 100% lifesteal ultimate, which also healed allies and was why he was purposely kept weak all that time.
And now Poppy is also losing her identity mechanics, which are both her stupidly broken ultimate and her retardedly overpowered passive.
And why is that happening? For the sake of Healthy gameplay.
Kalista should be no different.
Those "tons" of ways to stop her you speak of are basically Point&Click Crowd Control spells, which shouldn't even exist in this game, let alone be required to catch her anyway.