>some of the things that make ML code inscrutable are that (a) every tensor has a shape that you have to guess, and keep track of as it goes through the various layers

That's not inherent to ML though - that's a library design choice to have tensor shape be defined at runtime vs compile time. A while back I wrote my own framework in C++ and chose to go with compile-time shapes, which as well as preventing shape errors is more in keeping with C++'s typing. For a dynamically typed language like Python maybe runtime-defined types/shapes seems a more natural choice, but still a choice nonetheless.