Your second point is not relevant in regards to A320 and most modern jet crew crew oxy masks, whereby the mask regulator supplies the appropriate oxy dilution or 100% automatically (NORMAL position).
It is relevant since 100% O2 still will not supply the O2 at sufficient
pressure to assist breathing. 'Normal' is a mix of O2 and cabin air, '100%' is all O2, 'EMER' is O2 forced out of the mask under pressure to inflate the lungs at high altitude.
It is not a matter of the percentage quantity of O2 being delivered. It is the fact that the lungs cannot inflate to inhale the O2 with the reduced partial pressure at that altitude. I've flown GIV for 10 years. It has the standard 'modern jet' crew mask.
Your comment highlights my point about the masks that was pointed out to us during the course; most pilots think 100% will prevent hypoxia at high altitude. It won't.