Uhhh... finding it hard to see how people took the song literally and seriously at the same time... pretty obvious that Led Zeppelin did NOT see themselves as viking warriors conquering new lands... abundance use in cat videos provides scant evidence people took it overly serious.
I’d say the only question is that overly serious, proposterous rock (see: Iron Maiden, Black Sabbath) and revolution-as-pandering rock (see: Def Leppard, AC/DC) became such staples by the late 70s/early 80s that people might not have been sure that Led Zeppelin was in on the joke.
.. finding it hard to see how people took the song literally and seriously at the same time...
The only point of the music was to make you smile. Most were pretty lame but teenagers are not the most sophisticated people in the world and we liked them.
The link is to a list of some of the novelty songs of the 1950s
https://www.discogs.com/search/?style_exact=Novelty&decade=1950
They did write many songs referencing days of yore.