Being wacky and over the top is not quite the same thing as misusing real historical figures. Using real historical figures implicitly asks to take it seriously, then to make a farce does not have a compelling logic.
Since when? Lots of comedies have used real historical figures. When you saw Bugs Bunny taking on Christopher Columbus or Napoleon, did you feel you were expected to take it seriously? What about Jesus and Pontius Pilate appearing in
Life of Brian, or Moses, Nero, Torquemada, and King Louis XVI appearing in Mel Brooks'
History of the World: Part I, or Queen Elizabeth I and George IV being regular characters in
Blackadder?
Besides, this isn't about farce, it's about fantasy. I mean, come on, it's a universe where gods and magic and monsters exist. Like all myths, it treats the entire past as fair game for story material. It's not as if the Greeks themselves respected a realistic chronology in their myths. The show never claimed these were the actual figures from history; rather, they were fictional/mythic figures inspired by archetypal individuals we know from history.
Initially suspending disbelief for absurd premises is one thing. To accept self-contradictory premises is something else.
Being a farce one week and a supposedly serious character study the next asks a lot of viewer tolerance. It's why the DVDs for serious theatrical dramas never have a blooper real.
Actually there are quite a lot of shows that blend comedy and drama quite freely. It happens all the time in British television and film. Look at
Doctor Who or
Being Human and you'll see a blend of intense drama and farcical humor that rivals
Herc/Xena. Heck, look at Shakespeare. In
Hamlet, he goes from the wacky lowbrow comedy of the gravediggers to the intense bitterness and rage of Laertes challenging Hamlet within a single scene!