Pyboard's (v1.1/Lite/D SF2/3/6) has boot time about tens of ms instead of hundreds of ms of ESP32. Even for Pyboard's slower than ESP32.
I'm about to measure boot time on nRF MCU's.
About RAM : even 16 kB of BBC Micro:bit allows to do a lot of things in MicroPython, by using optimised software (drivers for low memory usage, etc), etc. For example, I've ported ulab module for BBC micro:bit, not yet published because I need to optimise the workflow for changing some source code files, then I've tested FFT for 512 float point numbers !
So 64 kB on nRF52832 or STM32WLE5, with a well developed MicroPython firmware and good practices, could be enough for many LoRa(Wan) node applications. Obviously some applications need a lot (even 1-2 MB) of RAM, so there is always a need of 'super-microcontrollers' for intensive Edge Computing, etc.