It will be a whole new story if new projects can start paying bounty hunters in USD or stablecoin
You've missed the whole point of paying in their coin/token.
The new projects that are not listed at exchanges and without their own market place will always pay in their own token (as long as there will be bounty hunters accepting that) because in this case they don't pay anything from their pockets. If the project has success and gets listed, you'll sell for other investors' money. If it doesn't have success, tough luck, you've worked for free. It's a risk the bounty hunter have to think of when he jumps for enlisting under their banner. One has to check first if it has a good enough chance for success and listing.
Absolutely right and there is no doubt about that many hunters worked for free in many projects.
Now days it's really difficult to earn from bounty campaigns. It's also risky work cause it doesn't matter how much good quality projects you choose, if they didn't manage an exchange for their coin after fund collecting, your work will be worthless. That's why many people leaving from bounty hunting.