What is the standard resupply mission time, 7 minutes? Minimum 3 runs to up a town? Troop runs.. No surprise it is the highest % use.
Reduced M3 effectiveness should be matched with an increase in object hardness, one set of bombers / m4 should not be able to WF a town. And if you reduce M3 resupply, a reduction in number of troops carried in M3 should be made (or number to take increased).
For me, don't care much about M3s. Know they are there and they are easily dealt with. The Wirble is a much more overused determint to fighting. Too easy, too effective, and the obvious first choice for a fight defense.