I'd say it's probably worse in terms of scope. The audience for some AI-powered documentation platform will ultimately be fairly small (mostly corporations).
Anubis is promoting itself as a sort of Cloudflare-esque service to mitigate AI scraping. They also aren't just an open source project relying on gracious donations, there's a paid whitelabel version of the project.
If anything, Anubis probably should be held to a higher standard, given many more vulnerable people (as in, vulnerable against having XSS on their site cause significant issues with having to fish their site out of spam filters and/or bandwidth exhaustion hitting their wallet) are reliant on it compared to big corporations. Same reason that a bug in some random GitHub project somewhere probably has an impact of near zero, but a critical security bug in nginx means that there's shit on the fan. When you write software that has a massive audience, you're going to have to be held to higher standards (if not legally, at least socially).
Not that Anubis' handling of this seems to be bad or anything; both XSS attacks were mitigated, but "won't somebody think of the poor FOSS project" isn't really the right answer here.