The thing with balancing is that it should have most to do with the $$$$ bottom line (customers buying DLCs, expansion packs, future iterations of the game) and maintaining a loyal userbase that will stick to the franchise. They have surely have identified which of their customers are the purely transactional (buy, play a bit, then move on) and then, the relational (COH community).
Competitive players like you and tournament organizers that generate buzz are also factored into their schema.
This means that the devs (who know it better than anyone) would segment their constituents, their userbase, their potential userbase, and allocate their priorities in satisfying them in that order.
So if 3 v 3 is the most profitable game mode for them, then more of their attention will be directed there than other mode and so forth. This is what I think anyway, as a business person.
In the end this is a business.
I happen to have played a decent number of 2v2 and participated in a number of tournaments in that mode as well. Soviets are in my opinion unbeatable in 2v2 atm if players play on a high enough level with no major mistakes committed by either side. Although it has little to do with the reasons you mentioned here, and even less with the M3.
It's also too "early" to comment on the balance in 3v3 and 4v4. Since there has been practically no organized competitions to decide what the optimal strategies are in those game modes. Although that might soon be changing.
As for the game itself 3 v 3 and 4 v 4 are very much centered around how well 100 pop cap armies are used in the 'war of attrition'.
IME, the Soviets fare better here and it becomes less about intricate tactical play and more about mass and armor. Munitions drops, and artillery are more dominant. The German small squad sizes tends to work against them in 4 v 4. Some of the DLC commanders are clearly optimized for 3/4 v 3/4 modes rather than 1 v 1.
I think many who play these modes are casual players (transactional) and they are pretty important to relic as well.