GTB has fog of war, so one of the aspects of attacking through three routes is that each route is likely defended to a different extent and by different weapons. One may have a lot of infantry in trenches, another som big laser turrets, so you would choose the route that seems weakest for your preferred units.
Right now there are no tanks for the defender, just turrets and troops in trenches, but I am considering a bonus mode where there is one big open-space battle between two sides, like GSB but on land. It would be reasonably easy to code, assuming the untis don’t do any fancy maneuvering and just head towards the enemy like a napoleonic army