Couldn't that last paragraph fit with that first paragraph? That Buck has taken all of his teams as far as he could, but they simply didn't quite have the talent to finish the job.
The 1996 Yankees brought in Tino Martinez to replace the rotting corpse of Don Mattingly's career, signed Mariano Duncan to replace Pat Kelly and Randy Velarde, and switched out Tony Fernandez for some rookie named Jeets. The 2001 Diamondbacks got a full Cy-Young-level season from Curt Schilling and swapped in Mark Grace for a platoon situation at first. Those are upgrades that he really didn't have available in his final season with those teams (even Schilling was traded for at the deadline in 2000).
But you must also question why did those teams make those moves AFTER Buck left. We all know that he has his favorites and stays with them perhaps too long (and players he won't play for whatever reason - Kim). We don't know how much input the manager has and in the case of Buck is it significant or not?
If Buck was a finisher then why didn't these teams make those moves while he was still there?????????????