The judge at my venue ruled that Hawk could not give Cosmic boy a click of healing if Cosmic Boy was already at full health. I have been using this trick for a long time and this is the first time it has been ruled incorrect. I would set up with Hawk next to any wild card member and on the first turn get Hawk off of his activation click.

Have I been playing it incorrectly this whole time, or was the judges ruling incorrect?

I would guess that you've been playing the ability wrong. To my knowledge you can't heal a character past their starting click which is what the move you're suggesting does. I would think it is the equivilent of trying to use support on a character that as already at full health.

Have never had to deal with this, but after re-reading the Titans TA...I would have to agree with the judge. Not sure why you think you could do one without the other? It says "exchange one click of damage" If a fig is at full health, he can't take a click of healing.

Your judge is correct.