Oh, blendOS uses cloudflaremirrors.com during installation, which points at the Arch mirror it thinks it closest to you, and installation should be quite fast in North America (the blendOS package repo's hosted in Germany, but it shouldn't be too slow and doesn't host too many packages required for installation). However, I do plan to make that configurable (as an option for users that know what they're doing, or perhaps through a CLI installer for advanced users), and might implement it in the coming few days.
(disclaimer: blendOS dev here)
oh yep, should've clarified, /system.yaml's, as the name might suggest (lol), for system-wide config only, and GNOME just so happens to support system-wide config (dconf and gsettings overrides); we used to have a utility for declaring config for individual users akin to home-manager in blendOS v3, but dropped it with v4 since that wasn't used much; still might make a return though :)
thank you for your support! :)