I like the idea, I have seen something similar being done with card games, where you fight on two or more lanes, but with armies like in this game it is something quite new.
Maybe the rng needs to be adjusted as sometimes I get all enemies on one side only for multiple rounds and I can't keep up, but with a bit of tweaking, some more upgrades, more units and synergies and maybe some roguelike elements I could see this being a very good game :D