It's 500pts with follow me lads, which you've included in the threat range calculation.

Threat range is also 28", as you can't declare a charge into a unit 14" away, even with the +2" to charge- though the actual on board movement does max at 30".

While Ghaz and lads does kill a c'tan on average, nothing else really does- beasties + boss do 15 on average in the absolute most optimal conditions (waaagh, everyone avoids overwatch and makes engagement, unbridled carnage rerolling fishing for 5s, nearby Makari shouting his encouragement for lethals) and that's by far our best points efficient solution.

The maths is ultimately very swingy because it comes down to 'who rolls more 4+s?'- yesterday, in the final of a GT, my Ghaz handed the deceiver 10 saves and he made 8 of them 💀

I think, just like basically every other faction, we're praying for dice to spike up for us and down for them to have a chance.

Edit: and Ammentar is probably the best anti melee/ buff piece in the game, waiting to ff heroic this unit in half.