I agree with Heretic, the BA are no OP but are definitely the best way to make score while giving the enemy team almost nothing.
I was in a game today, 1 vs 1, an Owens B vs a single BA, the result was the Owens always killing the BA, the score was like 8 to 0 but the BA team had double score and would have won at the end, then more players joined.
The money pumping side is also important, a BA can have everything, including a personal APC, with the default money, everything else can be donated, a huge advantage. If a BA is supposed to be equivalent to a Mech (5 CBT BAs) then costs and rewards should be comparable to mechs. BAs more advanced weapons should not be purchasable with the base money.