the other super saiyans that existed were ment to have destroyed themselves in their rage, and so it is perfectly possible that there wasnt many before, Pain you say that saiyans trainned for millions of years, and not 1 appeared, this doesnt exactly mean anythin, no saiyan had ever been as strong as goku when he arrived on namek, and he gained a LOT more power while fighting freeza, plus he had a lot more motivation that the other saiyans because he was kind hearted, unlike ur average saiyan, plus goku only got so strong cuz he died and was allowed to keep his body, and train with king kai, under 10x gravity, and then he was wished back to life, had a hard battle, then trained under 100x earth gravity, and no saiyan could of trained that hard because they never had the chance to..... they didnt have gravity machines, they didnt have dragonballs and they weren't good people and there for didnt have the motivation......... my fav was either cell games or buu saga because i like the monologues in them, like 16 and when vegeta is about to fight goku, plus i think the animation was better, and it had more interesting characters, in my opinion