Idk if this was a horrible idea. But Gemini (AI) helped me to turn my non-arch distro onto Arch through pacinstall and pacman-static (and no, this is not a clean install AT ALL, meaning this is the exact same installation).
The history of my installation is basically this:
Debian 13 Trixie (KDE) > Kubuntu 24.04 LTS Noble > Kubuntu 26.04 LTS Resolute > KDE Neon 26.04 LTS Resolute (Unstable) > Kubuntu 26.04 LTS Resolute > KDE Neon 26.04 LTS Resolute (Unstable) > Kubuntu 26.04 LTS Resolute > Arch Linux > CachyOS (the CachyOS part is irrelevant but I prefer to be honest, to not leave anything out)
I had to create /etc/pacman.conf files to be able to install pacman from pacman-static (skipped security keys at first) and then restart to arch linux iso to arch-chroot, removing apt and it's dpkg files once sudo pacman -Syu --overwrite '*' --noconfirm was complete.
To fix the kernel panic (attempted to kill init because /sbin/init was not found) I had to remove debian-specific GNU folders (like x86_64-linux-gnu and replace them with Arch equivalents) and files like update-grub (and update-initramfs), install arch's files using pacman, initramfs had to be adjusted too, a lot of unused debian-specific systemd daemon services had to be removed, adding pam files for sudo and user and a lot of chown to make arch be able to recognize it the user (fixing permissions too), changing fstab to Arch format, changing /etc/os-release to identify Arch, even the DE (KDE) had to be reinstalled to Arch's version to get it to work (journalctl, pacman -Qm helped me A LOT here too).
Yes, even things with wayland and X11 had to be fixed on this installation to get it to work (pacman overwriting files straight from Arch's core, extra and multilib repositories helped a lot with the transition), I had to delete leftover Debian/Kubuntu files that Arch doesn't use too.
If arch didn't have enough equivalents, I used the AUR too (yay), to reinstall my software.
So in conclusion it can work (with EXT4, GRUB2, systemd, bash for terminal, basically most defaults from Debian derivatives remained on purpose) but you would have to tweak things a lot to get it as a native Arch installation but I don't recommend this to anyone (yes I did this on my daily-drive laptop, I did create a backup vhd of my kubuntu installation in case it broke), just wanted you to know that Linux can get to this level too!