EOS is about return on time. I can install and configure Arch. For most of the machines I install, I would rather just use EOS since I like most of its defaults ( including Dracut ). Some of the EOS utilities are nice as well.
As you say, EOS is basically Arch once installed. So what is the downside?
Just having to hunt down and install yay on Arch is reason enough to use EOS to begin with.
I notice that CachyOS installs both yay and paru out-of-the-box. Nice.
I installed CachyOS on a VM ( Proxmox ) just to check out the OOTB experience and I am glad I did.
In a lot of ways, it is similar to EOS as you say. That is a compliment as I really like EOS.
The UX is a bit different though. Lots more blue than purple of course. On the command-line side the differences are bigger. It uses the fish shell with a jazzed up prompt ( reminded me of Garuda ). There are a tonne of aliases. They clearly like Rust as a few of the Rust core util alternatives are installed. They even alias ls to eza.
Both yay and paru are installed at install which is awesome.
The default file system was XFS. Btrfs and zfs were both options. No bcachefs at install but it is available after.