Man of La Mancha premiered in the Sixties. 1965 or '66, I can’t remember which. To replace it on your list, I’d include either My Fair Lady or West Side Story.
True enough Max, but but broke the Frankenstein Monster’s rule* in order to give the audience a cheap thrill (that, as you point out, is ultimately pointless).
*“Let the dead stay dead.”
I wouldn’t say it’s pointless… it reintroduces the “No Day But Today” theme which is the message of the musical. If it hadn’t happened, what would they have been singing then before the curtain fell?
“Ding dong the witch is dead.” 
Sorry, that was just a cheap laugh. I can never resist.
But what were they singing at the end of The King and I, which had the courage of its convictions?
Ooops. Right you are. I’d go with “West Side Story” a definite period piece that showed the talents of a young Leonard Bernstein and Stephen Sondheim.
WICKED could almost fit the 2000’s, except Schwartz has been around for 30 years.
I think it depends on the person. I personally thought it was a great musical. Great songs and great storyline.
As my roommate told a friend when we watched the movie,
Nobody’s gettin’ out of this alive.