Is it actually possible to win? I played a bunch of games with different factions and no matter what I did or how much I built up my army the enemy was always impossible to defeat.
Yes, it is possible to win. Smaller maps make it easier. The AI uses auto resolve. You can swithc to using it in the options. After some analysis it turned that auto resolve underestimates the occoured losses. The v83 version is probably going to have a difficulty option that tries to balance this with real battles.