"What you were doing was effectively operating system programming" is a _major_ stretch.
The sorts of programming you were doing was barely higher-level than the sorts of programming involved with an OSDev-style "Hello, world!" kernel[0]. My remark is not a stretch at all. At most you had a few thin conveniences (like having some graphics-related features already available to you, since Woz had prioritized that when he designed the Apple II's BASIC interpreter); beyond that, it was direct access to everything from RAM to tapes (unless you were running Apple DOS, but that was not at all required for BASIC programming on an Apple II, and the Apple II didn't ship with it).
BASIC for all intents and purposes, was considered a high level language when I learned it.
From what I remember, BASIC kinda had a similar reputation as PHP does today (probably unfair) in that it wasn't generally taken very seriously as a programming language. You didn't use BASIC to make real programs on an Apple ][. For that, you'd do it in assembly or machine language. That bias is still stuck in my head even after 3 decades.
The best my high schools had were the Apple II family and PDP mini computers -- my first high school course in BASIC (I already knew Basic from my home computers) -- we were marking up Hollerith cards with Sharpies. You don't know painful debugging until you have to manually scour a deck of optical cards looking for an errant black mark.
We did not deal with interrupts, memory access or low level components. What we learned was more about logic -- not much different than what I do today.
The closest I ever got to memory access in BASIC were the occasional peeks and pokes, and even then, you didn't need them to write a useful program. Being able to build something even as rudimentary as a CMS today on (insert language of choice here) is more broadly useful than anything I came out of high school with.
Also, remember that nothing was really cross platform back then. Most languages were procedural, and free databases (relational or not) -- forget about it. I was on Mac at the tail end of high school, and if you wanted a tool like Lightspeed C or Lightspeed Pascal - those were way out of the budget of a high school student.