My mech can do all of that in one stride, the second stride was backing up further and would probably happen at the same time as your character landing. Time isn't even the real issue though, it's more the difficulty of carrying out a throwing action after committing yourself to plummeting towards the earth. An ordinary human shouldn't even be able to note that the mech is moving and prepare to throw before hitting the earth.

I don't understand what you're saying about pinpoint accuracy, but in a nut shell, of course using a gun increases accuracy, that's the whole point of a gun. My sheet also says that computer systems handle pin-point accuracy, so it's not even my character's own precision. My mech was also standing still in optimal conditions and firing at a still target (centre of mass as well, not a super-leet headshot), your character is falling to earth at incredible speed and firing at a moving target. These scenarios are so widely different I can't fathom how you can possibly compare them. Also, the anti-tank gun is probably about four or five feet long, but you also have to take into consideration that it isn't particularly wide, making it a difficult target at the best of times.

Besides which, my character isn't even attempting to combat you while you're in the air, if I personally think that hitting a falling man plummeting towards the earth with -bullets- is incredibly unlikely, I fail to see how a javelin throw is very likely to work.