One unit per tile is absolutely ideal for a streamlined, quick, and efficient game. It removes the endless clutter of people playing large maps and having to manage like more than 10 cities in previous civ games, or fighting military battles with a large number of units. Indeed, it is suspected that few players in their right minds would attempt to play such "epic" games with a reasonable level of difficulty anymore because the task of managing units in those numbers and at those scales with a new system would be incredibly time consuming. This is all accomplished through the removal of the abstraction of the "simplistic" and "unfun" ability to group units in stacks and send them somewhere. Instead, it gives the player clear, direct, and easily used (and abused) options to outwit the AI in war at almost every juncture, and ensures an additional sense of "balance" and "fairness" where it's difficult for large empires to steamroll and conquer others. Overall allowing for additional focus on enjoyable gameplay.