The game does not demand you be good at all factions, just 2 of them.
You can ignore 50% of the factions (soon to be 60% with Brits) and still compete. Note in Starcraft, you can ignore 66% of the factions. After Brits come out, you can argue that the 6% doesn't even matter and the tournament format in SC2 is close enough to COH2 (not like it matters)
