o10, I hope you don’t read this as my joining frogman and "piling on". As you’ve noted more than once, you and I share many musical tastes and appreciations.
For all that, I think you look at classical performances in too much of a constricted view. If you really believe "when some guy played the same identical "Bach Concerto" as another guy the night before, and someone else the night before that, I don’t see any latitude for improvisation", then I suggest you read, or re-read, my post at 10:46 PM yesterday. Even as a non-musician I easily hear different interpretations by different musicians of the same written score, be that for soloists or entire ensembles. How else would classical conductors or orchestras develop such individual reputations? There can be and are improvisations in both genres.
Yes jazz and classical are very different, but those apples and oranges can all become "juice" for those open to the tasting.