...presumably you've never had the need to turn off the transponder either, yet these are things that happened aboard MH-370 that night.
Turned off, or failed, who knows for sure? I certainly don't. The suggestion that it was deliberately turned off is pure speculation at this point. The only known fact is that it stopped transmitting.
It is certainly possible that the left AC bus was de-powered for a time, I never said that it wasn't. However, your suggestion that it was deliberately de-powered in order to 'take direct pilot control of the aircraft' is, frankly, preposterous.
Further, it IS possible to force the satcom to log off a satellite from the flight deck, WITHOUT de-powering the system.