So if a tile is 100km wide and it takes my warriors 40 years to cross it, they are traveling at 2.5km per year? And that is supposed to be realistic?
Cmon people! If Civ used a realistic scale of size and time, you would have millions of cities and it would take many years just to complete one turn.
Please stop sacrificing everything at the altar of realism.
Most of civ is rationalizable.
Campaigns are telescoped, sort of like one of those magnifying glass extracts on a map. There might be a thousand years when nothing much happened, except this war right in the middle that lasted ten years. What civ does is take that war and splash it all over that thousand years, project it onto a larger screen, which is what they are going overboard with in Civ V it loooks like. As long as things that interact are on the same scale with each other that's fine. The mesh works well. Building one more unit during on the war time scale and one more unit on the history time scale mean different things, but they are standing in for each other. On the war timescale it means frantically raising some troops. On the history time scale, it means building up military infrastructure.
Also, very early eras where turns are forty years, represent a time when the movement of a unit represents the long term migration of a tribe. Even in modern times when turns are a year represent the movement of units represents the movement of a unit, as in all the barracks and military families and move, which really takes a long time. Sure the troops of the 82nd Airborrne can parachute into Afganistan in one day, but it would take them all year to actually translocate the division there as its permenant location, lock stock and barrel.
Similarly, a "city" represents a region, the premier city of an area, and each improvement is a smaller city, with this or that economic emphasis.
Clearly we are willing to compromise and adjust if we play civ, but I think there's been a lot of science or art or luck that went into making it something we can adjust to, and some of those principles should not be thrown out with the bathwater. Very little sacrifice is required, and innovation is still possible. Premodern ranged units should have a range of one tile, and there should be a nice simple two unit per tile limit.
Then we can see battles as magnifications of what is actuallly smaller onto a big screen. But when an archer somebody forgot to upgrade meets a long range mortar and they have the same range that will clash no matter what.