I don’t really think pax is the issue here, although pax is a bad specification in absolute terms. But “classic” (V7) tar just isn’t specified at all, and has plenty of its own differentials.
(Users also want things like filenames that are longer than 100 characters, for obvious reasons.)
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Hit up Wikipedia for tarball format and you may agree with me. It's a classic example of a standard where you look at it and go, "??? Who asked for that?". I'm not surprised the article focuses on pax when finding tar inconsistencies. Original tar is just fine.