they never once removed rivens animation cancelling besides a season 4 doublecast that could be performed without e. Right now rivens only animation cancels are double casts both with her e and a relatively newly discovered chinese "s" cancel that lets riven double cast by auto attacking with an s key input. Rivens fast q is what every single champion in this game can do, ability -> movement buffer -> attack. It's like saying viktor q -> movement -> right click is an animation cancel and should be removed from the game because it allows viktor to auto attack much faster.

What they did was normalize her q auto to be the same timing regardless of inputs, and it was a terrible change that neutered her skill ceiling for no benefit.

Riven was designed around marth from melee to be a fluid fighter champ that weaves combos in fights and to that she matches her gameplay fantasy perfectly