As you probably know, rek'sai's ultimate is dodge-able by most dash and flash like abilities in the game. There are other dodge-able ults like fizz, warwick, ashe, and malphite. The thing that makes rek'sai's so bad though is that the before mentioned champion ults are cast instantly without warning and, even though they can be dodged, require mostly prediction which feels fair for the one ulting and for the enemy if they do manage to dodge it. Rek'sai's ult tips the scale in favor of the target. It will always have a delay and audio cue that allows the enemy time to prepare to dodge it, especially at long range. The ult has a lower CD than other ults that would have more impact if they landed, but it still has an ult's CD. When it gets dodged it always feels like bs because there's nothing you can do about it as a player. It all depends on the enemy's skill and not your own. The fact that it can be dodged so easily by basic dashes like riven E, vayne Q, and yasuo E just doesn't feel right. It's too easy. And you gain no benefit at all and have to wait the full cooldown as if you did. The least they could do is have it refund some of the cooldown if it is dodged. This happens too often when playing rek'sai and even though you're still at a loss, with that change it won't be as harsh.