Agreed.

The VAX 9000 range tried to become mainframes, and the effort to make them bankrupted DEC.

But there are non-IBM mainframes. They do run under emulation on x86, but they are still real. Unisys Clearpath, for instance.

The CS course I did in the 1980s had us use a Burroughs mainframe for the first year (complete with MCP) - I think this was a cunning ploy to make us really appreciate Unix when we got to use for the remaining three years....

Just curious: in what ways?

I started out on VAXen before I learned DOS or Xenix, and frankly, I preferred it.

File versioning was wonderful and with that as a basis, we'd never have needed the vile baroque mess that is Git.

The Burroughs user environment was a thing called CANDE - which really wasn't much fun at all:

https://en.wikipedia.org/wiki/CANDE

How odd. That sounds very strange, but now I want to try it. :-)