You have to remember in air to air combat you need to have speed, altitude or if you have both it's even better. If your in the position to where you would have to pull a cobra you have sacrificed speed,altitude at that point wouldn't matter. Let's say hypothetically an enemy was that close behind you and you pull a cobra and he overshoots (miraculously not spraying you full of holes or running into you) and lets say again hypothetically you are able to get your nose down fast enough to get a lock on the bandit and squeeze off a shot and shoot him down, your elated until you realize that 99% of the time the enemy will always come in at least pairs. You now have no energy, speed, and altitude won't matter because you can't gain or lose it fast enough to evade an attack, the bandits wingman now has an extremley easy shot and YOUR DEAD!!! end of story...
I give credit to the Russians for having planes that can make those stunts and perform them well at airshows, but as far as actual combat you probably wouldn't be walking home at all.
