Just gonna link this old variant of go I made up that was designed precisely for games like this: Limitation Go (Variant) (alternatively War Go or Morale Go, idk what to call it)
And what you could do is make it so each capture is the same as a casualty, and whoever wins (either by points, resignation, or no men standing on opposing side) takes control of the territory, and all others will be forced to retreat (attackers from wherever they attacked from, and defenders from any friendly (or neutral if such a thing exists) territory
This will definitely cut down on a lot of the time, and allow more direct influence of how having multiple units changes the situation