Define sucks a little more precisely?
See, I would assume you mean that their musicianship is lacking live. Which is entirely possible, I'm not quibbling on that as I'm not into the band enough to have watched a ton it their live stuff to form a useful opinion at all.
But the way you described how they suck is about one member not being up front and visible. Again, I've never seen them live in person, nor watched a ton.
But I'm not sure that the lack of stage presence = suck. It sure can contribute to sucking live, but it isn't what I'd say is the determining factor.
It's like when someone big name in pop does a complicated and intense dance routine that's impossible to sing through. Is that a good live performance or a sucky one? I err on the side of it being a good show if it isn't all they do. The inverse is also true, that if all they do is sit on a stool and absolutely nail the music, it's a good show.
It puts me in mind of Iron Maiden too. Even when they're having a rough go of it musically, they can make up for it with giant Eddie and awesome lights and pyro and you still walk out happy enough even though Bruce was almost croaking (fear of the dark tour was exactly like that when I went lol). But when they're on point and the flashy stuff is there, it's a fucking spiritual experience.
My impression of tool is that they err on the side of musicianship first, and anything else is secondary. Was that maybe what you experienced?