The more important reason why it is a _horrible_ _stupid_ mechanism for software installation is that it is not _repeatable_.
It is well understood that casual .deb .rpm usage requires an equivalent level of trust as downloading anything else off the internet... but they have the added advantage of being _consistent_ _repeatable_ and _mirrorable_... I can copy the entire repository of any version of debian I want to my local file server, and use that to spin up however much infrastructure I want. And the only person I need to rely on after I have fetched the initial packages is myself.