quadra happened because riven did half the damage after lis flashed in, and the stun lasted a little longer because of riven chaining right behind her preventing any flashes = riven was a major part of the play. Granted, it was a good wombo combo initiation play between the liss and leona but that doesn't change the fact that the riven finished them off with her op aoe stun and burst dmg. Rivens kit does too much and for a fighter her burst dmg is stupidly op, and the damn cdr boots being more than just viable on her, but straight up op just adds salt to the wounds of her broken imbalanced state.
She needed to be more squishy and her shield nerfed more to account for that kind of mobility and damage output. Or the damaged needed to be toned down with perhaps a smaller aoe range.
I hope season 5 remedies this with the changes, we shall see.