56k Beware and Spoilers Ahead
I think it was safe to say before (and for a lot of) 70s, The tournament arc in shonen fight manga was relatively non existent, but it was extremely prevalent in Sports manga like Hoshi no Kyojin. Sure there was fighting in manga like Ashita no Joe and Tiger Mask, but those were more sports than fighting. You could say the same for Kinnikuman, but as the series goes on, it gets more and more surreal. It becomes less and less about normal Pro Wrestling. But where did the Wrestling angle come from? Short answer the Author's (Yudetamago) passion for Wrestling. Long answer, no one, at least outside of japan, knows for sure... If anyone has any translations of the author's interview pages (you know the ones that come with every manga or even american comic book ever made), please tell me so I can confirm any info. Back to the trournament arc, Shonen fight anime like the obsure but influencial Otoko Ippiki Gaki Daisho were largely episodic, heck Tiger Mask, despite being about an overarching tournament, was largely a fight of the week series. But things would later change when japan and many other western nations decided to boycott the Moscow Olympics...