First Picking Katarina support is actually really good.
Enemy team is gonna do some stupid shit like chogath mid, and is basically gonna just pick 4 tanks and an adc.
Enemy bot lane is gonna be retarded in the early stages of the game. Push really hard under tower and try to dive. Early dive = easy kill for support katarina since she is gonna have moderately high burst. Dumbass enemy bot lane are gonna go hard to kill ur adc. Melt them.
Late game she can never get caught with her sightstone. Enemy team gonna try to use all their cc on you alone. Leaving your adc and mid wide open.
Gg ez.