The trick, if you have the patience, is to play the earlier battles (in the first half of the game or so) over and over again, retreating before you completely win, in order to level up and just breeze through the final levels.
yeah, I actually didn't realize this until I got into later chapters...right now, it's not so much that I'm not winning battles, it just takes so damn long to move your folks into place, then the comp has to move it's folks, back and forth, back and forth