If you wanted more anti-tank, could you not just load up on some
MSU metamorphs with claws? There's not much they'll not be able to crunch through.
Personally I prefer the look of the brood cycle to the calvacade as it seems to play to the codex's strengths more - russes and chimeras aren't exactly awe-inspiring units, particularly as they'll be the focus of most of your opponent's anti-armour. It's interesting to see something different though!
I'm not quite as impressed on the primus's boost to the cult ambush table. For the cost of those primuses you could have 28 additional acolytes (or 20 additional metamorphs with the claws)
As an aside, including a flyrant or two would boost the anti-tank firepower, but it depends on what theme your army is going for of course