Yep. Not just that, but it has zero channel time, and you don't have a precise timer on its CD unless you saw the last use, know how much CDR she has, and bothered to calculate all of that in your head. At most you can work off of behavioral cues, and even then a Cass is likely to hold off until she has a good opportunity (in teamfights), much like a Sona, Leona, or Morg, and you're not likely to specifically watch a single champion when you've got other things going on (their assassins and tanks going in, your assassins and tanks going in, upkeep for whatever your role & champ require, so on and so forth).
Basically except for early fights in lane, you've got functionally no time to react unless you're lucky or exceptionally good at reading behavior. That's how most ults like that work; it's instant or near-instant hard CC which can only be no-selled (when on target) by great prediction and timing of escape abilities. Of course you could dodge it easily if it was mechanically DotA's Medusa's Stone Gaze, but it isn't.
TBH Putnam, I think you're getting a bit too caught up in your "LoL is worse at everything"... thing. There are issues with every -- LoL certainly has a substantial chunk of problems -- but the simple fact is that not everyone enjoys the same thing. I'm not comfortable with mobility creep in LoL either, but I also do enjoy a certain degree of high-mobility gameplay and skill-oriented balance in [insert-whatever-name-you-prefer-here-genre]. I watched gameplay of both DotA and LoL before I tried either, and I settled on LoL because it looked like more fun for me.
Also, unless I'm mistaken, Covenant was referencing the actual Medusa, the Greek myth.