The collision he experienced didnt exist
Thats what you need to get over. The collision realy did happen in his reality. And his reality is all he can react to and do somthing about. It is realy no different than shooting bullets , in the shooters reality bullets hit the plane. From the person being shot at, the bullets missed him.
All this is simply because of net lag, you see the person very close to his acctual flight path, but it is shown at a later time. So if you are standing still you don't percieve any difference, but once you start moving , realative to you , he is in a different place and same time VS the correct place, at a different time.
Checking them both could be done, but that would only ever happen on head ons. Therefore it would promote boaring right on threw the other guy wrather than evade like you should on a head on. Instead of giving the advantage to the guy who broke off you would give the advantage to the guy who didn't. Hence no one would want to evade the head on pass .
2nd on anthing but a head on both clients would never collide at the same time, hence when doing a diving attack you would just fly right on threw someone. I.E. would just be like not having a collisions.
Right now the system is both fair, and promotes proper play.
HiTech