The two other conditions listed in the page you link basically amount to "the buggy code has to run". Related, I think SSV [1], introduced last year, would also have blocked this bug even with SIP disabled. But none of that invalidates concern that areas of the OS we don't know about might not have the level of defence in depth that we would like - it's not like Apple has never cut corners or shipped bugs to hit a date.
1: https://support.apple.com/en-gb/guide/security/secd698747c9/...
One can have vague, general concerns about any operating system if one lets their imagination run wild, though, and one doesn't care about the presence or absence of specific examples supporting the suggestion that the "permissions system...makes assumption[s]" about SIP existing.
This is an example of defense-in-depth being present, and defense-in-depth still failing for some users who gave escalated permissions to some installers, allowing them to run roughshod over their filesystem permissions, leaving them vulnerable to a subsequent varsectomy. If one did the same thing to their Linux system, the same thing could happen.
https://arstechnica.com/information-technology/2019/09/no-it...