> Some birds of prey, such as hawks, are believed to have an acuity of around 20/2; in this respect, their vision is much better than human eyesight.

The scale of how good vision can be keeps going and going indefinitely (presumably until you get into physical limitations to resolution related to wavelengths). While 20/20 is considered normal and not in need of correction, it doesn't mean it's the best vision observed among human beings, or the best that's physically possible (for human beings or other animals).

https://en.wikipedia.org/wiki/Superman#Powers,_abilities,_an...

> I thought 20/20 meant you don’t need glasses or any other aids to see.

No, of course not. Try looking at Saturn at night. Then try looking through a telescope. Odds are you'll see it better with the aid.