Actually, they really had good writers who seemed quite knowledgeable about history. Their references to historical figures and incidents have always struck me as so much name-dropping, displaying little or no in-depth knowledge.
Take "Decomposing Composers," or the Philosopher Song; you say that they are historically accurate. Well, Plato was a philosopher, and Beethoven is dead, but apart from that, what are they accurate about?
As for "Oliver Cromwell," it's lyrics indicate nothing more than that one of them could read an encyclopedia article, which, given that most of them went to Cambridge, is not overly impressive.
OK, fine, but they were funny! And you can't exactly expect a windy discourse to garner yucks the way a short bit does. However, the scene from The Holy Grail where the King orders his subjects to "be quiet" "I order you to BE Quiet" "Who does he think he is" and then is given a lecture on government being brought about by agreement and consensus and not because a watery tart hands over a scimitar, is an astute and funny bit about government.(didn't he even explain they were members of a narco-syndicate collective, whatever that is). IMHO. V's wife.