As someone on the company response side of the HackerOne brokenness, I can confirm that this effect is real but would also note that the difficulty of distinguishing is not as severe as all that, because the companies have access to the source code which the researchers do not typically have access to.

This means that the token cost of verifying any given HackerOne report is dramatically lower than the token cost of producing a report in the first place. Automated triage systems should be possible, and realistically it's well within the capabilities of most companies to go further and actually automate the Red Team side of it and catch issues before they surface in the black box research. From what I've seen doing so should cost dramatically less in tokens than the bounty payouts do.

The problem is that security is woefully underfunded in most companies, so even an infosec organization that saw the deluge approaching from a distance may well not have had the resources to prep for it even if they knew exactly what actions they would take if they had the capacity.