Come to the conclusion that the first 2 or 3 levels just aren't indicative of how hard the campaign is going to be...
Space Marines on Very Hard, first level, not too bad, second level, pain in the arse, third level, equally big pain in the arse, fourth level, went quite smoothly, fifth level onwards, turned into a roflstomp.
Finally got everyone some armour and a couple of items that increase AR for allies too, Martellius can call in a dreadnought and spam a single turret. Ancient is now using a Lascannon and is basically shredding vehicles (and infantry) at extreme range and can call in huge artillery strikes. Cyrus is... well shooting everything with a sniper rifle. Commander is nearly invincible to small arms fire and restores allies health on hit and has just received armour with 'permanent infiltration' on it which is going to make assault jumping very funny.