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Rivals include the Arduino...

I would not say that Arduiuno is a rival. The popularity of Arduiuno and RasPi may be similar but they are two different worlds, you are comparing "microcontrollers" and "computers".

For example:
Ardiuno is based on a microcontroller, there is no "real" OS apart from some specialised microcontroller OS' like RTOS. Apart from Due (84MHz) all other MCUs are 16MHz or slower. RAM and internal flash memory is in the order of KB.

On the other hand all other boards you listed are running proper OS (linux/windows), all have frequencies in the range of 1GHz, RAM is external and is in the order of GB. Memory is usually on a separate chip from the CPU, for example on memory cards or eMMC flash.