[reincarnate0x14]

The two big problems with it were that a) the computer player coding was just shockingly bad at dealing with it, particularly around any sort of geographic chokepoints, and b) it was incredibly tedious to deal with moving more than a handful of units.

Many other games like Total War series or Age of Wonders dealt with the overall question by having split strategic and tactical game modes, and they're hardly alone in that. Civ5 and 6 tried to keep the bastard child of those two game concepts in the same strategic-map and it just doesn't work that well.

[recursivecaveat]

There are a lot of subtle consequences of 1UPT as well. You can't let the player produce too many units, or the whole map will lock up. You can't make units too expensive though, or they'll just be hitting next-turn 40 times between each production in the ancient era. So tiny cities have to punch above their weight, and big ones below. Once you do that though you have to heavily penalize expansion. What they really needed was to increase the tile-density of the map several times, give room to maneuver. That would seriously change the city management gameplay though, potentially make it too tedious.

[reincarnate0x14]

I can see a split of using large hexes for cities and strategic deployment but having 7 child hexes inside each strategic one for precise unit movement working out. Effectively limiting stacks to 7 units for combat, and also potentially letting a few groups of units move around each other with multiple turns of micromanagement.

The corp/army mechanic could also be tied into that.