For being a parallel to U7, Universe 6 doesn't really have many strong fighters

[HeroR]

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Just imagine if Frieza had shot Goku instead of Krillin or Piccolo on Namek. That would have changed everything.

But you're right, a lot of the gains Goku and co made after King Piccolo were under the patronage of a god. Even the Hyperbolic Time Chamber counts since that's not something they'd normally have access to without Kami or Dende. Up until Whis showed up, it sounded like Goku regularly popped over to King Kai's place for further training.

To note, if Goku never reached Super Saiyan, Freeza would have reminded the strongest in U7 with maybe the androids being stronger in a couple of years. U6 weakest can take hits from a base form Goku who smashed Super Saiyan 3 Gotenks.

Think about it.