While I agree that "combat as performance" exists, I don't think it can be equated to "combat as sport".
Combat as sport is about symmetry. Two teams square off on relatively fair terms and only one of them can win. That doesn't mean that your team will win. Obviously, a better team will typically win, and this will often be the players, but that's not necessarily the case. You can lose/die/TPK in CaS. However, poisoning the other team's Gatorade or holding their mascot for ransom would be out of the question (those are asymmetrical CaW strategies, which would be considered unfair in a pure CaS game).
Whereas in CaP, you arguably can't lose unless it's appropriate to the narrative. There are various ways of accomplishing this such as death flags, etc. Even Worlds Without Number, which considers itself an OSR game, spends a few paragraphs on how to implement such an approach, if desired.
I think you've actually landed on something fairly relevant. From what I've seen, people sometimes conflate CaS with CaP, and CaS folks can get pretty irritated when folks throw around adages like "no challenge" with respect to CaS. That's because those folks are thinking of CaP, not CaS.