You have to go Captain for the M15 HT to overcome OST's infantry superiority. Riflemen don't cut it against Grenadiers and Panzergrens. Yes you read that right. A 240 mp unit with a 60 munition upgrade is effectively superior to a 280 mp unit that pays extra to access grenades and BARs. Horay for balance.
Yawn... BAR'd up rifleman do just fine against grens. I know you're convinced that Grenadiers are disgustingly OP but they really aren't that strong prior to being vet 3 with their LMG's. You can quite easily close the gap and overwhelm them in a lot of situations.