No, it's terrible design. You should never be completely useless in an FPS, ever. Fuck stuns so hard.
Oh, I don't disagree, just saying that you can take her apart. Doesn't mean playing against her is fun.
Basically the same as my thoughts on Bastion. Sure, you can wreck Mei's shit pretty easily, with the right pick and the right strategy, but that doesn't make dealing with them entertaining.
Reinhardt can stun you in... 1, 1.5 different ways, depending on how you count his charge. McCree is legendary for his stun, even though it only lasts .7 seconds. Roadhog hooks you, you're stunned while that happens. Junkrat traps you in place, which actually technically doesn't stun you, since you can still use some abilities; Reaper can go ghost while he's trapped, for instance.