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

It’s pretty good IMHO. Greek symbols are all obvious. \Omega and \omega for upper and lowercase omega etc. Super and subscripts with ^{} and _{} also work with \sum and \int for indices and intervals.

Software like Latexit and Mathpix also help a lot.