It's funny but I've been wanting to make a post like this too for a while. Now granted so far I've only played with pumps or blowbacks but I find that the Piranhas I've used are just fine and push paint nicely and without any excessive kick. I found that the Custom 98, that everyone seems to say is THE woodsball gun to have, was no better at kick than my basic R6.
I also think there's a lot to be said for fine tuning the blowback to create a gun that cycles fine but reduces the kick to an easily dealt with minimum. That's one area that not many seem to have tried to work in.
I know that on one of my Piranhas I lightened the hammer a bit and the next step is a lighter delrin bolt. I've got it running on about 250 psi and it "sounds" like it's pumping ehough air during dry firings to hit the right velocity. Final report is waiting on actual chrono testing. But I think the biggest issue is that most blowbacks are designed with a heavy hand knowing that if they don't try to mess with it then it'll work. But with a little messing around I think there's some good playing to be hand with them and they area also compact and light in most cases.
.... or maybe I just like the underdogs....