And just to address your point about the idle, next time you're taxing out to the runway have a listen, the engines will be very high pitched and whiny. That's a jet at idle (perhaps 20k rpm, 5% throttle). Then when you're about to take off listen for a point where it turns from a whine to a rumble, this is the compressor stage bypass valves closing forcing all the intake air through the jet. This is full power but the rpm has only gone up about 1/3.