Mages aren't really underpowered, I've used them a couple of times and mages who are high-tier can do TONS of damage to opponents especially when attacking castles / towns. However, they die pretty easily and since you are part of the mageocracy, I highly recommend mercs for a nice mix of foot soldiers and cav.
(Mercs have high wage cost but once you're quite late in the game wages aren't a problem for you)