AFAIK the issue with using submodules is you still need the rights to pull the other source repo. However, you can use submodules or LFS to pull a specific build artifact from a build artifact repo or source instead of the source repo, which provides a neat way to manage the dep without fattening the main repo and allows the source repo to be kept separate and high security. I'd certainly do this before changing RCS/VCS solutions. That said, reverse engineering has become relatively trivial in the AI age so the practical utility of providing built rather than source elements is dropping.