> strict vetting process
Eh, don't expect too much from this. It's just the packager downloading a .tar.gz from the website or cloning the version control, maybe checking if it looks alright for a bit at most, maybe check signatures if they're available (or maybe not), and that's usually it. Especially for updates don't expect a "vetting process" of any meaning.
The main "defence" is time, not any vetting: usually people find out any problems before packagers have time to update the package or before a package becomes "known enough" to be added to Debian (or any other package repo): there will be GitHub issues, Reddit drama, HN threads, news articles, what-have-you.
Things like Chromium has a bunch of eyes, but that's the exception and very much not the rule.