All of high school is a waste of time just as you have always supposed.

I don't understand this point of view. Of course, if you're already intelligent, motivated, and a self-learner, high school won't do that much for you.

But as a college professor that occasionally teaches freshman, you can tell which students went to great, average, and poor high schools. Students that went to elite schools are typically confident in their own intellect, have honed practical skills (how to write, how to think critically, the ability to solve basic math and logic problems, etc), and have a firm grasp of basic knowledge that gives them cultural/social capital (about how our government works, general history, canonical works of art, modern science).

High school teaches you the basics, which some people can pick up on their own, but most people cannot. The very best students will succeed even with a bad teachers in a poor school district, but my heart breaks for the average students who clearly didn't get a quality high school education. They end up so far behind their peers that it's a struggle for them to catch up, and many don't. Seeing a clearly bright student with interesting ideas fail because they were brought up in the poverty-stricken neighborhoods...well, it's one of the most depressing things I have to face.

I try to meet with them individually, get them in contact with the appropriate resources, encourage them, but sometimes they find the distance between where their classmates are and themselves too overwhelming. And they shut down.

To say high school doesn't matter seems to me a privilege of actually having at least an average high school experience. You don't know the value of what you had.