It is based on nothing. It is not intended to be offensive, and it is not intended to be about slavery. Similarly how master and slave pins are not either, or how blacklist and whitelist are not about race either!
I grant it's not nothing, but I think it's not enough of something to make changes over it. Thinking of a master record or similar is the natural reaction when you learn about the terminology, and most young people have never used bitkeeper, so unless you go out of your way to explain why this is "bad" most people won't even know, so what do you gain from it?
BitKeeper, the VCS that preceded Git, used the terminology "master" and "slaves", so the association is not based on nothing:
https://github.com/bitkeeper-scm/bitkeeper/blob/0524ffb3f6f1...