Okay. Firsdt of all ... sorry, but the idea that speed is irrelvant is Nonsense. Your speed increases the force with which you hit (F=MA.) If you are falling standing, or falling while moving forward at 20 mph, you will Not hit with the same force. Sorry, it's physics.
Anyone who doubts this, have a friend drive you down the highway; when the car hits 65 mph, gently step out of the car. You will only be falling six inches so you come back and tell us about it. Thanks.
As for reaction time---it is partly training, partly reflex.
I Always fight to stay up because I Don't Like Crashing. Can't pinpoint why ... maybe the damage to the bike, maybe the damage to the rider ... some reason.
If I have time.
Some crashes have been so fast, I was hitting pavement before I could move ... maybe a slight twist, but nothing to mitigate the force. other times, I have used a variety of techniques, with more or less success. If I practiced more, I would do it more naturally, but still, some wrecks happen way too fast.
But not all of them. People can Claim that if I could fall with control, I could ride with control and stop the wreck. Those people simply do not know,. Others claim that there is never time to do anything but flop around. Those people simply do not know.
I have been riding on the road, in traffic, for fifty years. I have a bunch of miles off-road. I have crashed a fair bit.
Thing is ... no one needs to validate me. I live my life, so when someone comes along and tells me what I have done is impossible ... okay. Whatever you need to believe.
I will check myself, when someone I respect contests a point. Sometimes my experiences were real but my interpretations were incorrect. obviously I am not infallible or I wouldn't be writing in a thread about crashing.