If you watch olympic sprinters, they’re bent over to the same extent. I’m pretty drunk so this explanation might suck, but the front-heavy weight distribution that comes with it means its much easier to propell yourself forwards while sprinting.
Of course, you can’t hold your arms like that, it was just for ease of animation. But it’s not 100% totally and all-consumingly bullshit. Just like. Mostly bullshit.
The Naruto run is not bullshit, unless you don’t believe in the other bullshit in the anime. To get to speeds where wind resistance makes any difference, you need to be running in the ballpark of the fastest running humans are capable of. Not the fastest per se, but the same ballpark. And even then, in the real world, it’s only a minimal difference and the Naruto run is far from optimal. To make it necessary you’d have to run faster than any human can, by a very large margin. Maybe even an order of magnitude faster.
However, in the anime, the ninjas ARE able to run that fast. So if you take into account the inhuman basically “magical” abilities of the in-universe runners, it would definitely benefit them to lean forward that much to reduce wind resistance. In many scenes they are moving so fast they will jump between trees for 4-5 seconds of airtime without losing altitude. That’s fast. Not only would the Naruto run improve air resistance but it would also prevent you from flailing all over the place when you jump.
So anyway, that’s why you should definitely run like Naruto if you are running track in the 7th grade.