You probably aren't playing Flash right... The real use of running man stance is a good mixup potential. I usually use it after I knock down opponents, as I can use it to stuff wakeup attacks, and if they try to block I will just choose the button which they aren't blocking for. Good players will be able to block on reaction for this move, but it is pretty quick so it's not easy. I usually use Lightning Charge or Flying Uppercut to close distance, it covers a good amount of distance and has quick enough recovery to avoid getting hit by projectiles.