The problem space a full Linux SoC solves is very different from the problem an MCU solves. (Imagine a lot of real time io, interacting with a lot of peripherals etc....)
What's eating Arduino's lunch is the various mcus: risc v, stm32, esp32 etc...
The Arduino 1kHz busy-loop and ISR designs is not real-time or necessarily guaranteed latency.
RTLinux or FreeRTOS are guaranteed-latency OS, that can reduce timing jitter.
"Real-time" is another term hijacked by people that think it means the same thing. It was a disservice to students, but thankfully FPGA or Raspberry Pico io DMA with mcu parallelism can teach people to understand clock domain crossing.
Part of the Arduino appeal, was convincing people the mcu and application SoC problem domains were the same. They are not, and never were... Hence the new Arduino board dual chip layout is twice as bad in some ways. Cheers =3
What's eating Arduino's lunch is the various mcus: risc v, stm32, esp32 etc...