Peacetime does not supply the Luftwaffe's wartime lessons

Would a delayed war let the Luftwaffe rotate units to train replacements and concentrate on later fighter designs?

Only if it adopted practices that historically emerged from wartime losses, since extra peacetime alone would not reveal the same training problem.

Unit rotation and broader replacement training would help Germany over a long war. Those reforms historically answered losses and operational experience that do not exist during the additional peacetime years. The same limit applies to Japan's elite pilot pipeline, which widened only after combat losses forced a change. A delayed conflict improves equipment development more readily than it supplies lessons that had to be learned in war.