3D printers are becoming extraordinarily inexpensive. When you can get a decent 3D printer for a couple hundred dollars, it’s more important than ever to have firmware with impressive functionality that can run in the cheapest of microcontrollers.

that's why FluidNC is so great: https://github.com/bdring/FluidNC Designed specifically for teh ESP32, it's a ground-up rewrite of grbl for ESP32. I've replaced all my various firmwares across devices (not my printers- those run prusa firmware) I build or use (microscopes, CNCs, various stages).

I still like the idea of a microcontroller doing the low-level work mostly controlled by a higher level microprocessor/SBC but it seems unnecessary?

Why doesn't Marlin feature such resonance compensation then, except for "it has not been built yet"? I suppose Klipper does offload heavy computation to a multi-core Raspberry Pi as opposed to a single-core STM32F1 running at 32MHz generally.