They aren’t terribly intuitive, but they are much easier than alt-codes. If you’re a touch typist it doesn’t take long to memorize a reasonable number of symbol positions. I still can’t temember any alt-codes though when I’m on a windows machine.

Badly discoverable? Sure. You can vastly improve the remembering part by picking appropriate mnemonics. The Plan 9 keyboard file is a nice start, I think.

It follows a set of rules so you don't have to remember a large number of sequences but can often guess the right one intuitively.

    ASCII digraphs for mathematical operators give the corresponding operator, e.g., <= yields ≤.
    Greek letters are given by an asterisk followed by a corresponding latin letter, e.g., *d yields δ.

https://github.com/9fans/plan9port/blob/master/lib/keyboard

https://9fans.github.io/plan9port/man/man7/keyboard.html

There's a program (mklatinkbd) to convert it to a format usable with X11.

> you can do the same on linux with the compose key. But it isn't very intuitive, discoverable or rememberable.

Well, LaTeX itself is not very discoverable either