Manjaro-chroot and mhwd-chroot cannot hadle encrypted volumes (at least in my case). For non-encrypted disks, these tools are great. But generally chroot utility is not that difficult to substitute it with smth else, especially when it is required for one-time work.
As for the wiki page, I suggest to add the following line there (into the section listing commands before chroot):
mount -o bind /run /mnt/run
This helps to avoid quite annoying error "failed to connect to lvmetad" when running 'update-grub' script.
Also, sometimes the root of a user's problem is not a 'broken' bootloader, so it's a good idea to check /etc/mkinitcpio.conf hooks and modules for (probable) mess, and regenerate initrd image with
mkinitcpio -p linux_414_ (underscored just to highlight my kernel version, yours may be different). This must be done when chrooted, of course, followed by 'update-grub' command.
This wiki page is great but a little bit outdated, and the link there pointing to some 'forum discussion topic' is broken, so why not edit it to point at least here? Just a suggestion.