I would argue Evil mode (which Doom Emacs includes) is an implementation on Vim. Only instead of being an implementation in C, it's an implementation in Elisp.

I equate Vim not with the weird configuration language or source code of the original Vim project, but with the interaction language it uses – and Evil uses the same one.

Evil is more than "a vim compatibility layer" -- it is a reimplementation of Vim closer in spirit to nvim than anything else.