If you want to keep the diversity aspect in the ladder (which I agree is at least somewhat important to the game), then the only real answer I see is to properly incentivize the playing of weaker races in a way that is proportional to the incentive you have to play the stronger races.
As Seanny as pointed out, it is bad logic to assume that a better chance at a playoff spot is a relevant incentive. Im sure some of us take some pride simply in qualifying too, but obviously the biggest incentive that exists in this entire format is the chance to win $500. Not life changing money obviously, but a heck of a lot more than most of us are ever going to make playing any other video game. So ultimately, the objective for most people who care about making the playoffs isnt just to make the playoffs. The objective is to actually win something once they are in the playoffs. Adding additional wildcard spots for crappy teams doesnt significantly improve those crappy teams' likelihood of winning the big prizes.
A few possible solutions have already been mentioned in this thread. Giving out some nominal money or other prize for the top finisher of each race would probably help, but to actually make a big shift toward parity, there's gotta be some kind of chance for the stunty teams to win a big prize, closer to the level of what all the tier 1 races are competing for.
You could run a separate stunty cup along side the regular playoffs, and give out wildcards etc to fill out the regular field of 20 teams or whatever it is that are considered non-stunty, and then taking X number of stunty teams + stunty wildcards for a 8 or 16 man stunty cup.
Or you keep things as they are now, with 32 teams of all races represented in the regular cup, but then as the stunties get eliminated, they go into some kind of consolation-bracket tourney where they compete for the stunty championship. You could run this a few different ways too - for example, just having it be last stunty team standing in the regular cup, and if two or more teams end up "tying" for being eliminated in the same round, they play a quick swiss-style against each other, or something like that.
The other thing I agree with is that the format of the ladder overall is very favourable to the more durable and violent teams, so as long as clawpomb remains as effective as it is now, that probably wont change. I think there is a point to be made for the rez format (although I personally dont like it), but I think there are some changes taht could be made to how claw, MB and PO work together that would be fair and better for the game overeall
tl;dr - people care a lot more about a chance to actually win the tourney/prizes, rather than just making the playoffs, so any incentives for specific races need to be planned accordingly. And clawpomb is OP in this format.