Well, reality has to be part of the discussions as that is what an amp is reproducing, reality of an audio soundtrack.
Music and HT sound comes in short burst when analyzed on a scope down to a very small fraction of a second, unlike a DC signal
And, its power duration compared to a sine wave of 70.7% is a lot shorter, a lot shorter.
If a power amp can satisfy the peak requirements of a musical passage, perhaps all that has been recorded reasonably, with its continuous power rating, we don't need a dynamic headroom, right?
But, if it cannot, then, what do we need in dynamic headroom to satisfy the peaks? Perhaps, that depends on our individual listening practices and speaker sensitivity. Loud sound practices needs a different amp than something more on the normal side of listening.
There are no perfect amps out there, never will be to the specs stated of unlimited this and that, so, perhaps that should not be a yardstick even for discussion purposes.
Only the universe is unlimited, as far as I know.