I mean, if you want to use your system pacman sure. But you can just download the latest statically built pacman to do the large jump without issues. However i will concede that is more than JUST keyring update

Edit: another fun way to get around that issue pretty easily. Boot any up to date arch installer, mount the old ass system root to /mnt and just run

pacman -Sy

pacman --sysroot /mnt

Now just normal syu and the live environment pacman will update the old system, arch/pacman has a plethora of easy ways to get around what would otherwise be show stoppers on apt/dpkg :)