Lets not forget that ERB wrote these books and stories to be serialized in magazines as exciting cliffhangers to get the reader back month after month. His primary plan was to earn a living, something he hadn't done consistently until he began writing.His audience was largely people who were willing to suspend disbelief and be entertained with the mental popcorn Burroughs was willing to supply. Very often ERB's readers were unsophisticated folk who viewed Apes as powerful monsters who could tear a tarmangani limb from limb. The reader didn't know or care that the apes were shy,and at times, gentle folk who also could tear a tarmangani limb from limb. They were just fodder for ERB's story telling. Remember that Africa was still an unknown land in 1900. It was the time of explorers who came back from the wild places with trophies and tales of amazing sights.
Tarzan's vine swinging wasn't likely are even possible I suppose but so what. Heroes were and are required to be amazing.
I go to the movies to be entertained. I love The Mummy films. I have a relative that sits through the movies and tells all who will listen why that just "Isn't possible." But then she could suck the fun out of the circus given a chance.
Don