@broker people play gap because they want to play gap. They want the easy playstyle, huge cannons and experimentals thrown around. If you change the balance that it won't be feasable anymore on dualgap they will just start playing an even turtlier version of dual gap. Don't know which rating range you are playing in but I suggest you to host your own games on more dynamic maps with 8 people in the game at max. Everything above that will turn into a turtle/ ecofest.
But I think it is time I visit some dualgap and abuse the shit out of t2 bombers. I know it can work.