I'm not going to give my speculation because I know what happens and don't want to spoil it. But I'm finding it interesting that you saw similarities to Tezuka in Miyashita's art style. Mustache Astro Boy aside, I think practically every early manga artist was inspired by Tezuka in one way or another art-wise. But actually, I think Miyashita had a few other inspirations; he worked as an assistant to Yoshihiro Takahashi, author of Ginga Nagareboshi Gin (Tetsuo Hara of Fist of the North Star fame also started out as his assistant), and he was also really inspired by Hiroshi Motomiya, one of the original Weekly Shonen Jump authors alongside Go Nagai, and also Yoshihiro Takahashi's mentor.
I really want to look into more of Hiroshi Motomiya's works; his popularity was on par with Go Nagai in the early 70s and he inspired artists from Tetsuo Hara and Masami Kurumada to Tatsuya Egawa and Tetsuya Saruwatari, and yet his works are basically unknown in the West (the only one he did that I could find on Batoto was Salaryman Kintaro, and only five chapters were scanned).