It feels a lot closer to write for MCUs if you write for 16-bit programs nowadays. The only difference is that MCUs are much more barebone and so less managed, but the constraints set by hardware however is the most distinctive common spot.
You don't call the raspi an SoC, and it's debatable that you'd call a prototyping platform like Arduino an MCU. The MCU is the main Atmel AVR, Microchip PIC, or similar part that drives such a board.