I'll just keep things simple and say that I don't think that the number of units in a battle necessarily has anything to do with making the battles feel more epic. Nor are more units in a battle in and of themselves sufficient to convey a feeling of "epicness."
My sovereign all alone battling a dragon for survival, casting spells and resisting the dragon's fire abilities could well feel epic to some people.
Another possibility is that in a big battle with a few hundred units things don't end up feeling epic for some people but rather feel boring and tedious, with even more units to click on, advance a square or two, watch mediocre animations that take forever to complete, and so on.
Making the battles feel more epic and less bland is a worthwhile objective, but there's much more to it than scale. A lot can be achieved with a good, well balanced and strategically deep rule-set combined with good art direction.