Limiting stack sizes was a decent enough idea, but 1UPT was not the correct solution for a game of this scale. The pathfinding alone can be a nightmare, especially for the AI. That’s not to say it can’t be done, Gladius pulls it off quite well, but I always thought it was a poor fit here.
How about three units per tile for military units, or scaling the number of units based on certain techs? At first you just have a mob with clubs, but later you have a legion protecting archers. Later, infantry, cavalry, and cannon.
I thought 1UPT showed clear and obvious problems, even if some people ultimately preferred it to “stacks of doom”. I was very disappointed Firaxis just rolled out the same system without taking the opportunity to correct course or at the least tweak the other systems so 1UPT worked better.