I play 4vs4 with a team of friends all the time (allies factions), we win, we lose, but it rather our skill or the skill of the opposite side that matter the most.
Balance is rather ok to have fun with arranged team. The real problem is automatching with strangers and game play diversity.
For automatching :For the moment, there is not any real solution except building your own team and practice.
What hurt the most in team game is gameplay diversity or/and cheese tactics abuse.
Some combination of tactics or units tend to be redundant. We all understand that to win anything is fine. But those fine tactics lead to repetitive gameplay a.k.a watching the same movie again and again. Not very entertaining. A cheese win is fine sometime but a cheese win every match is boring for everyone.
A possible solution : Add or modify some commanders so there is a greater variety of «best» tactics to win.
Units/commanders while maintaining some balance must favor and reward innovative and sound gameplay.
Long live to COH2, the king of all team RTS.