In a realistic fight with superhuman elements, the only action Vos should have been able to make before the kick hit him was moving the dagger, and the only reason that would be possible is because it was already there. Even the crouching wouldn't have been possible before the kick hit him. 

All of it would be possible in a perfect character fight, but only because in that kind of fight the characters would have the same level of awareness as the writers and be able to react and think and multitask instantly. In a realistic fight the characters don't have that level of reaction speed or thought processes or awareness, unless it's stated that those are their powers.

With regards to the air burst, if he waited that long the leg would have dropped too far for it to work.