I remember people saying that Gnar sucked when was released. A couple weeks later, when people learned how to use him effectively, he became the subject of quite a few "X Champ OP NERF PL0X" threads. Pretty sure once people get over the trolling aspect of Kalista and actually try to use her correctly she'll be subject to the same treatment.
I'm not sure if the same will be said about Cass though. The Cass mains I've seen on the board seem to dislike the fact that she was reworked at all rather than her being weak in any way(which she kind of was, admittedly).
You mean AFTER they gave Gnar huge QOL buffs, like greatly shortening his cast times and giving his Mega Q an AOE?
People said Gnar sucked on release because he did.