Is that all? Will that remove all the traces of arch?
There will be some other minor dot files in your /home which you might want to review, like .bashrc, .bash_profile, .profile etc. These should be mostly harmless, but if you don’t recall customising them, then yeah free to nuke all the dot files. Also be aware that some programs also leave their configs outside the .config folder, like Firefox might have a .mozilla folder, GTK programs might create a .themes folder, vim has .vim. So you might want to review and delete these as well, if you want a clean config.
As for the last step - just before you boot into your new distro, you might to get rid of the Arch/Endeavour entries from your ESP/UEFI. Run efibootmgr to see your current UEFI boot entries, then nuke the entries using efibootmgr --delete-bootnum -b #.
And to get rid of the GRUB configs, delete your <ESP>/EFI/grub folder. I’m guessing your /boot is on your root partition? If not then you’ll also need to delete /boot/grub.
Now when you install your next distro, you should get a nice and clean GRUB install.