Except, their model is also to ship an AUR helper out of the box, despite the fact that holding back distro packages compared to upstream actively breaks AUR ones that depend on those in the core Arch repo.

If they bothered to do the same thing with the AUR that they're doing with the upstream Arch packages, it'd be one thing. But as is, basically they're claiming that their design keeps the experience "stable" despite the fact that this same decision directly causes other parts of the experience to become unstable.