Maybe by Manjaro's maintainers, but certainly not by Arch's. I've been using Arch for a little over a decade. The position that I've always seen in the official IRC channel is that forks such as Manjaro are explicitly not Arch.

Here's one of the oldest versions of the "Arch-based distributions" page on the wiki. It has a notice at the top that says that forks are not supported by the community or developers: https://wiki.archlinux.org/index.php?title=Arch-based_distri...