mhwd-kernel doesn’t work to install a kernel in chroot.
I don’t know why or whether this is documented in wikis.
I know this from experience.
Use pacman instead of mhwd-kernel to install a kernel while inside the chroot environment.
watch the output - whether the initrd is created in the process or not
depending on that do or do not do:
mkinitcpio -P
and
update-grub