IMO, it's problematic that players can have vastly different incomes solely depending on what faction they choose.
The entire unit balance is centred around cost.
Might sound drastic, but I propose all of the resource upgrades should be normalized and made the same.
I'd go as far as to say Faction Diversity currently suffers because unit balance is dependant on the economies being the same. Example: If I get 2 mass per tick, and you only have 1 mass per tick, it doesn't matter how factionally diverse the units are because I will have 2x as many units.