since you seem to be rewatching all of it i have a genuine lore question thats gotten muddied in my memory: was it that the saiyans had genuinely never figured out the concept of training to get stronger, or was it that being able to get stronger doing that was so rare/hard no one bothered?
I think it has to do with the type of training. Most saiyans were murderous barbarians who just killed shit and only got stronger when they were seriously hurt. Goku got access to fancy techniques on earth and in the afterlife. At least that's my theory.
This is probably the original intent but the Saiyans became much more civilized and hierarchal as the series went on. Toriyama also believes that in addition to training the body, you must have the right mindset and the right heart, according to interviews.
i think it mostly comes down to "the core cast are epic"