In fact many embedded requirements are not as complicated as a 3D printer and essentially consist of basic logic and state, sensors and effectors, potentially with some external communication. It may surprise you but 8 bit micros are absolutely fine for this and can serve HTTP at well over a hundred requests per second without breaking a sweat.

If you read the Stepper code for Marlin @ https://github.com/MarlinFirmware/Marlin/blob/1.1.x/Marlin/s... you will see it's nontrivial... bunch of PhDs implementing nontrivial maths in a highly constrained environment. That's cute but not demonstrative of real world concerns. In such cases, you would absolutely throw more hardware at the problem, eg. for motion systems maybe dedicating one 'dumb' MCU per axis and outsourcing planning to a more rational/powerful environment.