Actually, we can get more profit if we getting paid by the project's token / coin because the value can increasing if the project success.
Getting paid by stable coins is not always good, but at least it will provides you a guarantee of the reward value.
But by paying huntera with a stable coin would make the project at a disadvantage. Because just like you said above only if they're a success projects then it's a win-win for both parties. Having said that, getting paid by their own coins/tokens might not be the best thing, but if the value of the coin/token increases then you'll get a very good amount of payment.
All this time, I haven't seen that many projects were willing to pay bounty hunters using stable coin or any other payment method beside their own product. Still, having a stable coin would make hunters at least be at east about getting paid and all.