I would say SPM is a pure measure of skill. No single statistic is a pure measure of skill. A high KD with a low(er) SPM usually means they camp. A high SPM with a low(er) KD usually means they focus on the objective.
With that said, I care more about SPM than KD. It's rare for me to be lower than second on the lobby leaderboard. My SPM in kill confirmed ranks around 200000.