With the assumed size of hexes being many miles across, perhaps 100 miles, 1 unit per hex is totally UN-realistic!!!I actually like the idea of unit congestion, because its more realistic.
The Mongol horde just isn't the same when it's 3 horse regiments spread across 300 miles. What about D-Day? They crammed 150,000 troops into what is, in Civ, about 4 hexes? Napoleon marched over 500,000 troops into Russia! The Persians had at least and in different tiles. I don't get why some are so opposed to the idea building a large SOD. A "SOD" is just another term for what in the real world is called an "Army". 100,000 at Thermopylae...etc etc. History is filled with mega-battles, not the little skirmishes we get in Civ5. In Civ5, you can no longer use such armies.
There were problems with the SOD, primarily the combat resolution 1 unit at a time. This was tedious - but exactly the same as in Civ5, only now we have far less units Virtually the entire economy of the UK was, for over 5 years, geared to churning out military units, so why the complaints about doing the same in previous Civs? It was the implementation of a large army consisting of different unit types in previous Civs, not the concept, that was at fault.
A straightforward fact: realistically, at the scale of Civ5, a hex should be able to hold HUGE numbers of military. How this is done is the question...and the Civ5 way is far *less* realistic than previous - it is a totally abstracted game mechanic.