" “Primary” and “secondary”, or whatever, carries the intent just as well."
Primary and secondary doesn't do that. Perhaps "controller" and "controllee"?
Personally, I think this is a stupid non-issue to raise any kind of fuss about. In the end, though, as a stupid non-issue, it's no more intelligent to fight against changing the terms. My only concern is that whatever terms replace it are both correct and don't coopt a technical term used for similar, but different, purposes, thus causing confusion.
Master/slave has the advantage of being very clear and well-established, eliminating confusion.