That's really only the case if you're installing packages from the AUR that are unmaintained or have a lazy maintainer. With the recent python3 switch, everything not in AUR (since that is user maintained), was updated to point to the appropriate python executable.
OR, the issue is that you're performing selective upgrades. Which, in that case, of course you're going to run into library issues. ANY rolling release OS is meant to be fully upgraded whenever an upgrade is performed, otherwise you risk breaking everything.
With Arch, it only breaks if you break it, since you have total control over everything.