Interesting list.
IMHO though, I feel that you aren't taking advantage of the tyranid prime fully without a warrior unit. From what I've experienced with Nids, they are heavily reliant on synergy between units.
Thats just how I see it though
I couple my prime with a unit of 9 warriors with deathspitters for a sort of "central synapse" unit that people steer clear of.
My trygon and mawloc are there to pop up and die... whatever is shooting at them, isn;t shooting at the rest of my army.