This is a Brit problem more than a OST balance problem.
I've been playing Brits exclusively (1v1) for a couple of weeks now and they really struggle at dealing with heavy support weapon play as their low movement speed makes them terrible flankers. The lack of mobile arty means they can't counter barrage or smoke outside of a fixed radius. The mortar pit is overpriced and can generally be ignored or destroyed pretty easily.
Really, there's no reason to do anything in their build order other than stall for a Comet and farm its vet 1 ability. Once you get there, you can turn the game. Everything before that is a slow death spiral.
