nah bane knights are better for gaspy, why i hear u say, simple - REACH
thralls have 0.5 melee, banes have 2 melee, means you can suround a model with more banes able to take a strike against the target.
Banes all fair badly vs high def targets, their mat of 6 is quite poor, however this is remedied by taking and protecting Bane lord tart. he can curse a target (for free without roll and without impacting anything else he can do, including swing and kill) which will give banes +2 move and +2 to hit vs the target.
The good news is you can bring bane lord tart back from the dead with Egaspys feet so even if he dies he'll be back to hurt.
High def targets are usualy quite troublesome for most cryx players unless you can debuff or boost.