I had to come back online to set-up my Switch (which finally got here). I've played a little bit of Mario Odyssey, and slowly getting a hang of the controls (I still need to commit the dive actions to muscle memory).
I got back on the forum way too late to actually contribute to a discussion about humans vs. saiyans, but I enjoyed reading this. Really nice job.
What I struggle with in Dragonball Z is deciphering what was an intentional lore choice from what was done out of necessity to make minor characters relevant. Gohan's had his potential unlocked twice but still struggles to turn super saiyan by Resurrection F. Master Roshi couldn't take on King Piccolo and win, but he can participate in the ToP, where every combatant should be faster than he can see (considering they've made a point multiple times in the series of saying that power levels also correlate to perception, in the saiyan, Frieza and Cell sagas, and Roshi should be SO far behind by then). The humans and Piccolo apparently get much larger power boosts from training with King Kai than Goku did, yet when they train for the androids, they seem to comparatively not grow at all. (And also never learned the Kaioken or spirit bomb for some reason.) So which is it?
I'll tackle these one at a time.
The thing about Gohan is that he doesn't really like to fight, so he doesn't train for fighting unless he needs to, at least not until after Resurrection F. Even if his Potential was unlocked, if he doesn't keep up with his training his body will weaken, and likely, so will his connection to his Ki. After Resurrection F, he realised that if he allowed himself to get too soft, then there might come a time when Goku and Vegeta
aren't there, and he's the third strongest fighter, so what then? Now he trains to protect the things he cares about.
With Master Roshi, one of the things about the series is that, even when someone thinks they've reached their limit, they can always push a little harder (basically the running theme of the Tournament of Power). In Dragon Ball, Master Roshi thought he was as strong as he could be, but Goku, Krillin and Tien showed themselves to be able to surpass what Master Roshi thought was the limits of mortal men, so he started training in secret (Goku even says this in Super, I believe it was in the Yurin episode, something along the lines of "So you've been training in Secret, huh, Master Roshi?")
About training for the Androids, Piccolo, Krillin and Tien
did get way stronger (Piccolo wouldn't have been able to deal with Dr. Gero like he did otherwise), they were probably stronger than Goku's base level (in theory), it's just that Goku also has Super Saiyan (a 50x multiplier) so Goku can become multiple times stronger in an instant.
Finally, regarding Piccolo, Tien and Yamcha not learning King Kai's techniques, they
were only on King Kai's planet for half the time Goku was there (Goku was on the planet for a whole year, while I think Tien, who I believe was revived last, was only there for about 6 months, Piccolo was only there for about the time it took for Bulma, Krillin and Gohan to reach Namek, which I think was a few weeks). Piccolo barely even engaged with King Kai in the short time he was there, just meditating under the 10x Gravity inherent to the Planet. At best, Tien probably learned either the Kaioken
or the Spirit Bomb, but not both, and has never actually needed to use the one he
did learn; I'd assume he learned the Spirit Bomb, if he learned either at all.
