... Are the Saiyans not the only ones hiding here?
Could just be their natural culture, damnit. They don't have to be secretly manipulated by aliens or secret societies in order not to innovate.
Human potential I define interestingly -- they improve much more slowly, but unlike Saiyans, they have no cap. I draw this from the series, where although the Saiyans rapidly outstrip their human contemporaries, they consistently hit walls in their training that they must transform to overcome. The humans, on the other hand, keep improving and improving the longer they go. Reference the "Resurrection of F" movie, which made the point that Krillin is only insignificant in the company he keeps, and is easily one of the strongest fighters in the universe.
I actually don't think the humans improved slower through training than the Saiyans. They never had a problem with dramatically increasing in time for the next budokai or keeping proportionally up with Goku (well, not until he got Korin's
actual magic water), it's just that they never got Zenkais that made them like 30 times stronger then stacked Super Saiyan on top on
that and they never entered the Room of Spirit and Time.
..Also, more questions. Sorry!
Have any of the Lords or Scions ever tried to go beyond Super Saiyan? For that matter, how much do they remember about any of the more advanced forms? Would they be able to tell a true Super Saiyan 2 from the form Vegeta used against Semi-Perfect cell?
How did they come to identify as Saiyans? I don't think Gohan and Pan ever did (at least not more than they identified themselves as humans/hybrids), and I'm not sure Trunks would either. Also, when did Vegeta's line and Goku's line interbreed? Pan's generation, Mako's generation or later?
Are any of the Saiyans ever born without tails like Goten and Trunks?
How accurate is their knowledge/stories of the Z fighters? Also, since Vegeta is a pretty big hero, how much do they remember of Goku's adventures before he learned he was a Saiyan? How much do they remember about Roshi, for instance?
This question probably isn't very relevant, but was Instant Transmission and Kaio-ken passed down or did the Saiyans re-invent them later?
Also, this last question is about the backstory and the answer could possibly be spoilers (possibly something to do with Gohan's message to Mako?) Why didn't they go to Namek? Did they simply not have the coordinates of New Namek and no one with instant Transmission who'd ever been there, or were they afraid going to Namek would be too predictable?