ERB had all the literary merit of a Bazooka Joe comic, but what a story teller. The man could suck you into the most absurd and illogical tales-and never lose your interest for a moment.
That's a writer!
To Hell with uplifting literature, the name of the game is entertainment, and ERB could do that. He had the guts of a burglar, too, he ripped off "The Prisoner of Zenda" in the most brazen act of piracy since Blackbeard, while the ink was still wet on the original. (OK, that an exageration) Maybe he liked it a lot, or needed some money. Mickey Spillaine used to write a new Mike Hammer every time he wanted a new boat, hard to tell.
The more you analyze ERB, the more you injure the willing suspension of disbelief(Sure, Tarzan taught himself to read while living among monkeys. And decided that he should shave with his Daddy's hunting knife, apropos of nothing a'tall. Not frackin' EVEN!).
Stories like this are like music, to be enjoyed, not analyzed! Those who can write them are a treasure for the ages.
Though it can be fun to take a wonderful mechanical toy apart to see how it works(the innards of the Magic Eight Ball are illustrated by Wikipedia, but be warned, it'll never be quite the same for you, the mystery is gone).
Let us love ERB's wonderful, impossible Barsoom.