But these `setup`, `loop` and `delay`, as well as the terrible "IDE" are central to the "simple" user experience of Arduino and are, imo, false friends. Teaching people busy loops and blocking behavior from day 1 is counterproductive because you'll have to unteach them later and jump through hoops to avoid them. Arduino libs are strongly optimized for "easy", not efficiency and flexibility.
I did just fine and so are millions of other people.
Using Arduino will not magically rot your brain and make you unable to ever learn other things. It will however get you started quickly and therefore give you an in. I started using Arduino in a student job, then used Micropython, did my masters thesis on using Micropython on cubesats and now I run a team of 15 hardware engineers.
All of this happened because I got started with easy beginner tools. There was no one to teach me the "real" way. The people preaching the real way and railing against simple beginner stuff usually don't write tutorials, build easy to use devboards or write easy to use libraries.
The thing you are hating on is pretty much this file: https://github.com/arduino/ArduinoCore-avr/blob/master/cores...
Arduino is C++ with some boilerplate and a library.