Music notation is a form of assembly language in which the original compositional ideas are expanded and flattened out into reams of tiny instructions for a "virtual machine": an abstraction of a musical instrument.
Nothing in music indicates semantic concepts like "this is motif M3 from the first movement, but transposes into a minor key, and played backward at half tempo". It's all just expanded into notes, which are like micro-instructions for the violin or oboe.
The music composer, when engraving notation, rarely invents any new symbols. If so, in a modest quantity.
In even small scale software engineering, the symbols unique to a given software system outnumber those in the programming language. We develop software by creating large dictionaries of new identifiers, such as functions and types. These symbols, which can number in the thousands and beyond, cannot have one character names, or there will be chaos.
The main challenge is understanding a program's own identifiers, not those in the programming language.
Terseness in the programming language helps at the microscopic level. The leaf terms of the program's syntax tree become more compact. The advantage of this in the overall context of making a big program is modest and has diminishing returns. Giving the core functions of a language short names, say from around two to six characters, goes a long way toward bringing about a useful level of terseness.
What also helps understanding is giving meaningful names to intermediate values. A pipeline of 13 operations is hard to understand, whether their names are one-character glyphs or 4-8 character words. If it's broken into, say, three smaller pipes, the first two of which are evaluated into variables with meaningful names, it will be helpful.
So that is to say, we shouldn't be cramming so many open-coded steps into a computation that they need one character names in order to fit into a reasonable space on the screen.
This is the problem with APL programs and programmers: failure to decompose complex operations into small functions with clear names.
I don't care that you can make some cool operation by stringing together seven letters. I am not impressed. What I don't want to see is you copy and pasting those seven letters all over the place whenever you wish to invoke this cool operation. If I will have to maintain that, I would really appreciate it if that string of seven letters appeared in one place as a definition, and had a nice ten-letter name, which is then used in all the other places where that operation is required even though (horror of horrors) it is 42% longer!
And, no, do not be giving it a one-character name using some Greek or Japanese symbol not yet claimed by APL. Do you really want your maintainers to have to make flashcards of the program's identifiers and do spaced repetition night after night?