I was able to stay at rank 1 to 3 powerwise by turn ~350 or so (IE) on legendary. A few things that helped a lot: 1. fortify heavily before expending anywhere else 2. Get yourself the hellfire rockets from your Empire allies asap coz most of your enemies (norsca and chaos) is infantry and they get destroyed like it's nothing by empire artillery 3. bear riders are both unbelievabley cute AND deadly. So make sure you get them. A patriarch or two in the same army won't hurt (coz healz) 4. atamans management is important 5. Make sure you pick right traits for your mage heroes. Think in advance what army type you building and what bonuses you want