Records are erased after each training period. Normally, only emergency procedures are flown, not normal routes. And they are administered by the airline, not the pilots.
That is as clear a hypothesis as any, and you are right... no oxygen at 35,000 means less than a minute of conciousness.
The restrictions for items to be boarded is nearly identical worldwide; the number of times the pilot has flown the route is not really pertinent. He would not have chosen the route to fly, it would have been provided to him by his flight dispatch department.
I would offer that Malaysia, like many of the other global carriers, have exceptional training programs and commanders do not qualify without having served a long apprenticeship, typically 10-15 years. The Asiana accident was a significant anomoly and experience in a particular type of aircraft or route is not really a valid metric.
Not without the consent of his copilot, which is highly unlikely.
I don't know about the tracking issue, and I am certain that if the airlines could disarm the PEDs, they would have done so years ago.
Just a simple switch. Not certain as to the "why" of turning it off. Makes no sense.