No, you are right. EndeavourOS is about two-dozen packages on top of the Arch repos and AUR ( 80,000 packages ). Most of the additional packages are just nice-to-have utilities you can enjoy or avoid.
EOS ( EndeavourOS ) is more of an opinionated Arch installer than a stand-alone distribution. Other than theming, almost everything in a fresh EOS install comes from the Arch repos. Even the kernel is native Arch.
I happen to like the way EOS sets up the system, including that it installs yay by default which makes the AUR available right away.
You can disable the EOS repos in EndeavourOS if you want. It really is just Arch.
I have started using Distrobox + Arch as well to get the AUR in other systems. I quite like Chimera Linux for example but it has few packages at the point. Distrobox + Arch / AUR solves that perfectly.