Healing may not be 'terrible' on controller, but it will never be as fast or efficient as a keyboard. Someone please correct me if I'm wrong.
You have casting time as well as a GCD, which is all the time in the world to pick a new target. I guess some people are just super slow at hitting up and down on the D-pad.

Not to mention in 8-man content if more than two people gets hit with something it is almost always more worth it to use Medica which requires no targeting.

This is just another factor of player skill. You might be better with kb/mouse but I am terrible with them but great with a gamepad.