what is psionic blast
The answer is simple. Blue, by tradition, isn't the color of aggression. It's on the other side of Red and Green and thus were designed to be more passive and controlling. Psionic Blast is one of the exceptions where planeswalkers could do direct damage to kill a creature or opponent. Combine with other blue control cards, PB is very dangerous, compare to Char is already in a damage-abundant color. Last but not least, there are also way fewer creatures with protection from blue than red.