Well, unless he was totally destroyed, that's it. Beside, it doesn't mean he can't be sealed.
He broke free but it's also stated that Gremmy didn't care. Knowing Gremmy's strength, if he wanted, he could've destroyed him at any moment.
Viability doesn't mean he can live in space or chocked to death into water.
"Major powerful". Basically, he just had a raw-strength power-up. His shikai still is the same & he doesn't has Bankai.
Indeed it must help but still, at least every captain could deal with him. Hitsugaya can't froze him. Mayuri can do whatever he wants. Even Kensei could punch him all day-long probably.
Shaz may be a tough-guy with his ability, but he probably isn't that strong.
Beside, he had a plan ? Trying to get the Hogyoku ? The Hogyoku AIZEN has in his body ? That's like the dumbest plan ever.
Oh no sorry, he wanted to CREATE one. That's even more dumb.
I agree to say that he may be stronger that most of Vice-Captains like Hisagi, Isane & others.
But he didn't stood a chance against some as Rukia, Ichigo, Renji or even all the captains.