IIRC many of the built-in tools were updated from FreeBSD in the last release, but they'd still be different from GNU.
Brew is pretty terrible though. It's slow, and doesn't handle updates/versions/dependencies all that well.
I've had it make major (with breaking changes) updates to random software when asked to install something unrelated.
HOMEBREW_NO_AUTO_UPDATE=1
HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK=1
export HOMEBREW_NO_AUTO_UPDATE HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK
brew is fine. Not the best package manager, not the worst one either.
You use nix or brew (or something like MacPorts).
And they are mighty fine.
You shouldn't be concerned with the built-in utilities.