FETs are basically integrated circuit switches.
CMOS on the other hand is a way of making integrated circuits.
I'm pretty sure most FETs are an on/off sort of thing. This is why you have a drive frequency in your esc setup - the esc gives you partial power by switching the drive FETs on and off. The ratio of on to off controls how much of full power you get. The drive frequency is how fast it switches.
The control circuitry is the programable part of the ESC is not the FETs. The FETs are used to amplify the signals from some other control logic, possibly a embedded microprocessor like in a
Schulze u-Force .
Here's a link to the plans for a simple airplane speed control
SC6