Comment by sowbug

The system guaranteed that a key signed a package. That was its entire utility.

At best, it defeated plausible deniability for package maintainers who had avowed public keys, but then somehow signed a bad package. This wouldn't have stopped the malware from getting onto your system. It only would have led you to the hapless (but honest) package maintainer.

It didn't stop someone who is not you from generating a PGP key for Richard WM Jones, signing malware, uploading to PyPi, and then disappearing back under the rock where they live. And if you believe this system is not useless, then you also believe that at least one person out there was not dissuaded from installing that malware because "Hey, someone named Richard WM Jones went through the trouble of signing it!"

As is often the case, the value of this system depends on your threat model. I'm not too worried about someone going rogue from the tiny population of people who were using PGP correctly. But I am worried about using a platform that claimed to have signing infrastructure, when that infrastructure had no meaningful checks on who was signing.