My understanding, and I fully accept that you have a far deeper knowledge than me and feel free to correct me, is that the fleet was much smaller in the TOS times than the TNG/DS9/VOY times. Only 12 Connie's were made in the TOS age (which was, what, 20 years into the Connie Lifespan already?) and then they were replaced with Excelsior as the heavy duty all purpose ship in the TOS movies era.
Well, no, all we know is that there were 12 of them in 2266/7. (Or 13, depending on whether Kirk's "12 like her" was meant to include the
Enterprise itself.) They could certainly have built quite a few more in the subsequent 18 years. Obviously they
did build more along the lines of the refit, since the E-A had to be a pre-existing ship that was renamed. And we have evidence for several others -- two more were glimpsed in Spacedock at the end of TVH, several were indicated on the Operation Retrieve graphic in the home-video version of TUC, and the wreckage of at least one was seen at Wolf 359 in "The Best of Both Worlds" (proving that they weren't entirely abandoned in the 24th century).
http://memory-alpha.wikia.com/wiki/Constitution_class#Ships_commissioned
http://memory-alpha.wikia.com/wiki/Unnamed_Constitution_class_starships
My understanding of TUC is that they decommissioned the A because of how badly damaged it was (the Klingon Torps going right through the hull) and didn't want to extend resources to repair an older, limited model when they could put them towards the more common Excelsiors.
That was not stated in the movie itself; it's a fan rationalization. In fact, in the movie, it was the command crew, not the ship, that was supposed to be "decommissioned." As Kirk's closing log entry said, "This is the final cruise of the starship
Enterprise under my command. This ship and her history will shortly become the care of another crew." So the makers of TUC didn't intend the ship itself to be decommissioned, at least not permanently. (I think ships can be decommissioned and then recommissioned for another purpose, or with a new name.) The fact that the E-A was retired and replaced wasn't established until
Generations three years later.
Fans have often speculated that the Enterprise-A and the rest of her sister ships were retired as a condition of the treaty with the Klingons - a sort of spin on the Washington Naval Treaty which meant it made sense to scrap the older cruisers in the fleet and replace them with newer Excelsior-class ships.
Although the Connie at Wolf 359 argues against that -- unless it was pulled out of a museum and put back in service for the emergency.
This would also make sense of Kirk being "rewarded" with a shambles of a ship, herself years old and requiring extensive work by Scotty just to become operational. She wasn't retired due to damage - it was clearly on the cards for months given the Enterprise-B was launched a year or two later, and Starfleet hadn't had time to assess the damage before ordering her to be decommissioned.
It was longer than that. The Okudachron puts
The Voyage Home in 2286, though that doesn't make much sense since it's only 3 months after TWOK/TSFS, which were in 2285 (and Kirk's birthday is generally presumed to align with Shatner's, March 22).
The Undiscovered Country and the
Generations prologue were in 2293. So there were 7-8 years between the launch of the E-A and that of the E-B. Not very much, but certainly a lot more than "a year or two."
On second thought, Morrow wasn't that bad, he was just doing his job. He doesn't deserve to have Trump projected onto him.
Few people do, granted. But how much do we really know about Morrow? We only have two scenes to base an opinion on, and they give the impression of a hidebound, unimaginative, narrow-minded individual. At best, he's not one of Starfleet's greats.