I think this idea would only increase the problem. Right now I feel the HT barely wins over the MED in direct combat, but just as you pointed out, in the HT, it's harder to land every shot.
I think one of the reasons the shots are harder to land is because of the double barrels; the two barrels simply can't have the same aim, so you'll miss a shot or two in a pinch.
I feel that right now the outcome of MED vs HT is thus dependant on the 'skill' of the HT driver to land every shot with his two barrels. If he can, HT wins. If he misses some, MED wins (Offcourse dodging and maneoevering play into this as well)
A HT ROF increase and damage decrease will actually increase the skills needed to operate the HT, whilst leaving the MED for what it is.
Ultimately, I think Push has a point (I mean the guy is busy with APB balancing 24/7). This may be the best balance possible without making one of the tanks useless.