The reason you need benchmarking software to load a PC CPU is because they have an operating system and driver software that will automatically put the CPU into a low-power state when there's no threads queued up to run. If you're just using a simple desktop program, the demand for the CPU is far below it's total capacity so it's almost constantly being put into a low power mode.
An Arduino is much simpler, and much different because of that. There is no native multi-threading, and also no automatic power management. The CPU runs full speed all the time. If you want to conserve power by using the low power modes, that's something you need to do in your program.