The premise that "fucking companies are misers" operate on that I don't share is that vulnerabilities are finite and that, in the general case, there's an existential cost to not identifying and fixing them. From decades of vulnerability research work, including (over the past 5 years) as a buyer rather than a seller of that work: put 2 different teams on a project, get 2 different sets of vulnerabilities, with maybe 30-50% overlap. Keep doing that; you'll keep finding stuff.

Seen through that light, bug bounty programs are engineering services, not a security control. A thing generalist developers definitely don't get about high-end bug bounty programs is that they are more about focusing internal resources than they are about generating any particular set of bugs. They're a way of prioritizing triage and hardening work, driven by external incentives.

The idea that Discord is, like, eliminating their XSS risk by bidding for XSS vulnerabilities from bounty hunters; I mean, just, obviously no, right?