Not all ultimates in Overwatch are created equal, this is reflect in how some ultis take more or less time to charge them others.
Wiston ultimate never scares me though. It's somehow disruptive but «being annoying» is hardly a hallmark. Yes, he can kill people with it… eventually… if the enemy has no healing… or escape… or a way to fight back…
But more important than a low damage output (he is a tank after all) it's all quickly he dies. A discord orb plus Roadhog hook combo it's sometimes all it takes for you to be almost dead. I never feel really tanky with Wiston unless I'm fighting a bunch of Lucios.
Not saying it should be buffed or not, it's just the difference between the presentation of the ulti and it's actual impact is a bit underwhelming.