Why exactly are hybrids stronger?

[Fox666]

My post is not showing, so I am going to re-post:

A liger is twice as big as a lion or a tiger, and that's an anomaly involving growth genes. That's surely less suitable for hunting.

[Bussani]

Vegeta states that Saiyans retain their youth and their hair doesn't grow more than a certain length because their bodies are suited for battle and because they're a warrior race.

So the fact that Trunks', Goten's and Gohan's hair grows like humans and the fact that they age normally suggests that their bodies aren't designed for just battle like pure Saiyans. So how come hybrids are still stronger and have more potential?

Because hair growth and how fast you age has nothing to do with hidden potential. Besides that, we don't really know if the hybrids stay in their prime longer or not since we never see them get old enough to tell.

[Herms]

But he's not talking about the Super Saiyan of legend, is he? Because I think he uses "chou Saiya-jin" when referring to Gohan, and when the Super Saiyan legend is introduced, Vegeta says, "suupaa Saiya-jin".

He doesn't seem to be talking about any legend, since he makes it sound like "Super Saiyan" is just something he came up with on the spot. It's like when Goku names Super Saiyan 2: "This is a Super Saiyan that has surpassed Super Saiyan. 'Super Saiyan 2', you could call it". Which is kind of a contradiction since it doesn't seem like Nappa has ever heard the term "Super Saiyan" before, when later the Super Saiyan is supposed to be a legend that even non-Saiyans know. You could work around that from an in-universe perspective, but out-universe it probably shows that Toriyama only thought up the "legendary Super Saiyan" much later.

I think it might have been different in the anime, but in the manga Nappa says Suupaa Saiya-jin, but with suupaa written only in katakana, as opposed to what we later see in the series where it's written with the kanji chou but with suupaa in katakana above it as furigana. Most of the more recent video games have started writing it out just in katakana like Nappa does. "Chou Saiya-jin" is what Freeza says in the anime when he's thinking to himself about Saiyans being a threat to him, the first time the "legendary Super Saiyan" concept is really hinted at in the series. In the manga it's written Suupaa Saiya-jin in what becomes the standard way, but I guess Nakao or maybe whoever wrote the anime scripts didn't notice the furigana.