That's a feature. You want a set of vetted and curated packages you can trust, and you want to receive security updates on them.
Distro repositories are a great example of 'secure for ideal users'. They give you security if you can put up with a small selection of software and older versions. In practice, we end up working around distro repositories by installing stuff with pip, or PPAs, or downloaded from websites.
Yet Amazon and other big tech companies have a very similar process of packaging open source software for internal use and relying on "outdated" libraries.
> I sincerely doubt that Debian can provide adequate security to its almost 50,000 packages.
There's a security tracker where you can see how quickly packages are assigned CVEs and patched - sometimes even before the upstream patch is ready.