I'm as form-critical as anyone, I suppose, but a few minutes with a Greek
Synopsis will show that Matthew and Luke didn't hesitate to work on the
Greek of the "Jesus" they read in Mark; so we can scarcely attribute every
nice piece of Greek to the unknown translator(s) of the tradition, and
blame all the poor Greek on Mark.
I know you admire Mark as an interesting and imaginative writer; but you
often speak of Mark's Greek as if he had written the Apocalypse. But maybe
we are just thinking of different passages as typical. (I recall your
saying that Josephus wrote superb Greek; and I used to give passages from
him on Greek exams as examples of some of the most crabbed Greek you could
find! He had some wonderful editors, or "assistants", who polished lots of
his work very handsomely; but he obviously lacked the talent himself,
unless you follow the theory of his gradual progress toward elegance (of
which one of my teachers, Ralph Marcus, used to say nasty words).
Anyway, I hoped you might move Mark up from the bottom of your list a bit,
at least above the Johannine Apocalypse, and above the Gospel and Epistles
of John. I guess I'd probably stop the elevator about there.