As a US 4v4 player whose build centers around rushing AA halftrack then AT halftrack out onto the field, securing VPs with MG bunkers and mortar bunkers, and then getting a sherman ASAP, I have to say that this is probably a build that I would be eating for breakfast.
Number one, Sherman curbstomps the Wirbelwind utterly. On an even game, I'm able to get a Sherman out onto the field at 12-13 minutes. You have about two minutes to bully my infantry with the Wirbelwind while getting shot and penned at max range by my M3 AT halftrack before the Sherman hits the field and removes the Wirbelwind as a serious player in combat.
Number two, if you don't go for a Wirbelwind, and instead for a Marder, not only do you have no good way to deal with my close-medium range specialist riflemen, but my M3 halftrack that's already on the field can hit and pen you from max range, forcing you off the field and putting you on the back foot.
Number three, you're giving up on the nebelwerfer, which while it isn't an infantry blob rape god like you might want it to be, the explosion+flames make quick work of bunkers and MGs inside buildings, which I tend to rely on to hold points
Number four, you're giving up on the Pak 40, which the only other efficient non-mechanized counter to MG bunkers.
Number five, you're giving up on the medical halftrack. Enough said about that.
Number six, if you try to get panzershreck Jagers in order to pre-empt my early Sherman, I'm going to walk on you with my riflemen who can suppress you with their vet 1 ability.
