This is an excellent game, my only suggestion is to maybe when pulling someone from the bench, have the ability to see possible dps difference between the pulled unit and the one you scroll over to swap out. That would make it slightly easier to decide how to set up your formation.
I found the spear guys could destroy most matches easily just as long as you stacked all of them in one area and ignored incoming troops from other areas. then just drive that one force hard. I won every match with them once I started doing that.