Now I don't know much about coding, but I do know that even Rome Total War several years and years ago, with thousands of units on screen at once, could pull it off. So I'm sure Elemental could pull it off as well.

Long story short, desynchronized animations. Meaning that when units move, or even just do their idle-animation, they are slightly desynced to not look like identical robots moving in perfect harmony. It looks incredibly artificial to see soldiers in a group move in exactly the same millisecond. Something more akin to Civ4 or the above mentioned RTW where they have a slight delay as they all move from tile to tile would improve immersion a great deal.

Note to the auto-naysayers, this does not mean slower animations or slower movement, it simply means that each individual unit model does not take the first step at the exact same frame.