A couple of MGs (one for each side) are enough, then what you need are Partisans with LMGs inside houses. A mortar is an option I would consider too (just leave it at the center of the bridge and it would out alone pinned squads).
Garrison buildings is the core to win the game, especially on the left side of the map. Try to get your MGs and the partisans with LMGs into them, the AI will constantly fight them instead of grouping at some point and pushing you. The key factor to win is saving munitions and spending them wisely (mostly to repair your tanks with PRTS Partisans.
Also, save after each wave starting from 12-13 so if you lose you always have a chance to do it again
Relic made this change to the ladder system, so if you are not liking it there is nothing we can do, you should direct your concerns to them. That being said, we totally support the change because it's a way to encourage teams to play (it also creates some competition and potentially allows us to seed better teams when we organize tourneys)!
In the future I'd like to see this system further improved by dividing the pool of players that are searching for 2vs2 (at least, I don't mind about 3vs3 and 4vs4 due to the past experiences on COH1) as a team and those that are alone (random players): it would certainly increase a bit the waiting time but at least we would create the foundations for a better competitive scene for teams that could play ranked games expecting to fight only against other teams (and on the other side those who play 2vs2 alone would have way more chances to win because they wouldn't have to be faced against teams)