Ellison's original script was published in a book called Six Science Fiction Plays
. I have that book and have read the City
script a few times over the years. My impression is that yes, it was a really good story... but just not Star Trek. The characters were not quite "right" - not themselves. The Guardian wasn't a character in its own right (I've always considered the Guardian to be an intelligent life form of some sort); instead, there were 3 "Guardians" that were sort of mystical aliens who gave clues and hints which Spock, of course, was the one to figure out once they went back in time.
It was too mystical, and the characters were off. Still, there was enough for the writing staff (or whoever was responsible for the final aired script) to work with.
If the version of Ellison's script I read is the last one he turned out, it shows he really should stop screaming about this - he really didn't
get what was wrong with it to make it a proper Star Trek episode.