> Alternatives like the Pi RP2040/2350 and Espressif's vast selection of boards can fill the gaps, but Arduino was what got me and many people I know into microcontrollers, so I have a special fondness for them!

Exactly. For the people who did not follow a structured educational program on embedded programming, starting with an SMT microcontroller was very hard.

Arduino made this fun and easy with their language & IDE combo. Typing some code and seeing the lights on the board reacting is a hell of a drug.

Once you mastered the IDE, you could either program other microcontrollers in the same IDE, or at some point you hit the limits and started digging into the vendor-specific toolchains.

If I started again today, I would again start with an Arduino.