I'm guessing your memory of a vendored-in error message is from Homebrew 😛 I never looked into why you shoudn't install them wholesale into

/usr/local

or whatnot, but with the embedded brew there's no difference compared to the submodule. Absolute worst case, if there was a difference, the formulas allow for some trickery/hackery. I have confidence we can figure something out where the submodule isn't needed