1) Fair point. The problem-solving technique is the most important part, but from this physicist's perspective, there is work that is objectively wrong, and there is basically always a limited set of solution approaches and results that I'd consider fully correct. Making the leap from "right answers" to "right thinking for decision making" is the key indicator of the expertise we want to train, and it doesn't happen just by making feedback less clear ;)

2) True! You really have to be careful even within terminologies. There are lots of different implementations of mastery-based grading, for example, and they're subtly different.

And a final note: we're of dangerously similar (but not quite the same) perspectives! https://www.youtube.com/watch?v=ANNX_XiuA78