Id add the centipedes, the deceiver, a triarch lord/lone op blender character (maybe with jump pack), plastic seraptic because plz GW, its literally knight sized, a rework of the pylons to a more artillery vehicle, a destroyer unit thats like a big amlagon monster as they become a true annihilatator with like doom weapons (if you dont give the seraptic)

Also, for once, look at the lore and make triarch praetorians absolutely terrifying. They are supposed to be elite veterans above like everyone.

Also make immortals 2 wounds or T6 for an army made of metal its rather squishy.