in many ways, warbossess are better in CC. A warboss (with klaw) and gargantuan squiggoth are the same strength, AP, and I. And a warboss is WS5, while a squiggoth is WS2.
Squiggoth is 5A base, 7 on the charge, which is only slightly more than a WB's 4/5. And there's always stomp.
Squiggoth is also T8, which imo is too low. It's a dinosaur the size of a mountain and is as tough as a 3" tall wraithlord. If anything in the game should be T9/10, I'd think it would be a gargantuan squiggoth.