How can a site be so based?

No, that's not what I said. I said there is middle school shit on Khan, which is true, but that there's also more advanced sections like calc, linear algebra and deqs.

What are the advantages over a good textbook though? He has videos but there is no way they can cover all of the topics that, say, an ODE book covers unless there are hundreds of videos on that topic alone

there's a system of points that constantly rewards you for watching videos and doing exercises.
Kinda like duolingo, except duolingo doesn't work and khan academy does.

it's partially but i find the way the quizzes and information is presented is a lot more intuitive than most textbooks

Almost done with Algebra II.
Should I learn Statistic and Probability or Calculus next?

There are quizzes as well which are actually the best thing about the site. The lectures are praised because brainlets can't learn from textbooks.

Trig

how based is Sal Khan?

I've already learned that.

Then learn it again.