OK, I haven't watched the video yet, but one important thing is to curve your rocketjumps (if you are not doing this already).
A decent soldier can predict your flight path and airshot you if you don't curve the jump, but if you curve it he will more often miss.
Also in bball you should avoid trying to rocket jump to the cap when the two opponents are aiming for you. Preferably they should both be dead before you jump.
Regarding tr_rocket_shooting2, there is a lot of things one can practise there. The first thing one should do is to is to become a flawless juggler. Shoot them at their feet and then hit them one or two times in the air. After a while one should be able to do this and almost never miss.
Then one can make it more difficult. I try to rocketjump, then shoot a rocket at someone from the air and then hit him with a second rocket as quickly as possible. To do airshots while you are in the air yourself is often more diffucult than if you stay on the ground.
To lead the targets while your own position in the air is changing is also very good training.
Then one can practice shotgun aiming. Shoot the enemies up in the air and try to finish them off quickly with your shotgun before they hit the ground. Or make a rocket jump, swich to the shotgun and try hit hit a specific target while in midair.
Then you are right in that there is a limit to how much you can learn only from this. It is after all bots (even if most players are almost easier to hit than those bots..).