It is not "no true scotsman" to point out that tons of projects are put on GitHub etc. without caring about whether others will actually be able to download and "install" and use the code locally, and that it's unreasonable to expect ecosystems to handle those cases by magic. To the extent that a Python ecosystem exists and people understand development within that ecosystem, the expectations for packaging are clear and documented and standard.

Acting as if these projects using whatever custom tool (and its associated config, by which the tool can be inferred), where that tool often isn't even advertised as an end-user package installer, are legitimate distributions is dishonest; and acting as if it reflects poorly on Python that this is possible, far more so. Nothing prevents anyone from creating a competitor to npm or Cargo etc.