There is no other Arch-based distro that strives to achieve a "rolling-stable" release.
Alternatives like Fedora have already been mentioned by other comments.
Debian testing is not a rolling release. Its package update strategy is focused on becoming the next stable so the frequency ebbs and flows around stable's release cycle.
manjaro since it manages to be less stable than Arch specifically because of their update policy
This is false. Their delayed updates mitigate issues in latest packages. Plasma 6 was released late but it was a lot more usable, for example.
I mean why even be on Arch if you can't use the AUR and have the latest packages?
Anybody who wants Arch should use Arch. Manjaro is not Arch.
Some of us don't want the latest packages the instant they release, we're fine with having them a week or a month late if it means extra stability.
There's nothing magical about what Manjaro is doing, it stands to reason that if you delay packages even a little some bugs will be fixed.
Also you can use AUR on Manjaro perfectly fine, I myself have over 100 AUR packages installed. But AUR is not supported even by Arch so it's impossible to offer any guarantees for it.
There's also Flatpak and some people may prefer that since it's more reliable.