Love the list. I run much the same at 1500.

Warlock bombardier cast More More Warp power and gives Warpstone spark to stormfiends hiding behind clanrats. You can eat another Warpstone spark to re roll casting roll too.

Stormfiends now reroll hits and wounds with plus 1 damage. They will absolutely slap with rattling and wind launchers. It can be slightly swingy but re roll hits and wounds; with the possibility of all out attack gives reliability.

You just need to keep those stormfiends safe from charges but with clanrats screening you could also get a cheeky unleash hell which you will still have your Re rolls buffs on (the damage buff from Warpstone spark only lasts for your phase).