check out touchdesigner, it has the ability to go deep into GLSL and python but is also quite approachable. i feel like it is generally regarded as a node based graphics programming environment, but would argue that it is really just an arbitrary real time data handling system that happens to have a lot of built in graphics nodes.

I've never found pd nor max to be productive.

why not? i use neither but they both have rich histories as audio programming tools. autechre are/were heavy max/msp users at the forefront of IDM, max for (ableton) live is a popular thing, and i have several friends who write pd things that then get run on their eurorack modules.