If the registers are abstracted away, you're left relying on other people's code. I suppose learning microcontrollers can mean different things to different people, but as for becoming a professional embedded developer, micropython and Arduino are dead ends. There is no transition to truly understanding the hardware.
We use MicroPython commercially so my perspective is different. :) I do agree with your intent though; just because you're using a high-level language it doesn't excuse you from learning how the hardware works.
However, if you do know the hardware, if you are familiar with what's going on under the hood, then MicroPython allows you to write the majority of your system significantly faster.
This is subject to change, as embeded developers now focus on writing lower or higher level code mainly in C/C++ as the industry migrates away from 8-bit MCUs to 32-bit ARM and RISC-V. Of course you're relying on other people's code, as you can't expect everyone to write their own RTOS and standard library and also achieve an acceptable time to market. Most embedded hardware products use an existing RTOS and build upon it. Understanding how the hardware works always helps, but most of the time you don't have to dig to register level to do that.
Micropython and Arduino are not dead ends but hobby grade tools.
