I think we're using the word "maintains" differently. Packages in Sid have no guarantees that they'll work, no security team, and no support system if you get stuck. Sid isn't meant to be used as a daily driver, and if your computer stops working that will be expected in Sid but a gigantic bug in Arch.
> Debian testing should be just as stable as Arch stable
Sure, but how up-to-date is Debian testing when compared to Arch?
> Packages in Sid have no guarantees that they'll work
Guarantee is a strong word. Can Arch guarantee this? Occasional breakage is bound to happen with bleeding-edge rolling releases.
> no security team
Weaker guarantees than stable, but that doesn't mean Debian doesn't handle security issues in unstable or testing. It'll be too late if they start dealing with security issues once a package enters stable.
That shouldn't matter much for people who're willing to use Arch as a daily driver.
> if your computer stops working that will be expected in Sid but a gigantic bug in Arch
A gigantic bug but still happens nonetheless.
> Sure, but how up-to-date is Debian testing when compared to Arch?
According to repology, Debian testing has twice the number of latest packages than Arch official [1]. Considering that packages of higher importance tend to be more actively maintained, I'd assume that Debian won't be significantly behind the latest release for packages that exist in both Arch official and Debian.
> Debian testing should be just as stable as Arch stable
Sure, but how up-to-date is Debian testing when compared to Arch?