You've had it explained a large number of times, but seem incapable of hearing the answer... so I didn't bother expounding what you've already been told over and over again.
But, to take your example, you fly kick a "rampaging knife guy", that's not self defence.
Is it reasonable use of force? Actually, that's debatable... in order to use the kick, you need to have come in from a distance, and most likely used it by blindsiding the guy with a knife. It might be considered defensible, but it might also look like a form of aggravated assault.
Might you get arrested? Yep.
As far as "very few people say they train for reasonable use of force and legal arrests", where on earth are you pulling that from?
What do you think self defence is?