I minor tweak for build diversity.

Deaucalion

One way to improve build diversity would be to free up the order in which you are able to upgrade into more powerful units. Instead of tiers, you could gain access to a unit by building the appropriate "wing" onto your main base. Each wing would also unlock the upgrades pertaining to that unit, which would help to filter the amount of information new players need to worry about.

This system would also work well if Artillery decided to allow squads access to a slightly larger pool of units, since it still limits the number of different types of units a player has during a single game.