Using Linux is simpler. Grub needs to replicated a ton of stuff that already is in Linux and it has worse more insecure and slower implementation. Once you hav

Using Linux is simpler. Grub needs to replicated a ton of stuff that already is in Linux and it has worse more insecure and slower implementation. Once you have a real Linux you can use all the battle tested code. You can easily and in good environment implement all the features you want in terms of boot verification, boot security, authentication, attestation and so on. Using Grub and pushing ever more features into it is not simpler, and its not more secure. Using a well tested Linux software that has long supported these features with a set of standard open source implementation for all the features you need.