I don't agree about the technically Arduino part. While waiting for my 1st Uno to arrive I read the main site docs. Arduino is an open, inclusive system.
I use pinMode() in setup but I'll read or toggle PINs in loop() for speed.
If I can compile it on the Arduino IDE and it runs, that's enough for me.
What it isn't is raw beginner.
Portability of Technical Arduino? Going from AVR to ARM, port hardware has some different steps but I am okay with coding for AVR especially along families like ATmega48/88/168/328 that are pin compatible and plug into an Uno.
Meh