I think it depends more on how you play the job than the job itself. If you just throw up med 2 or succor and just focus on the tank you may only get a comm from the tank. If you involve the rest of the party you'll probably get more comms. This is just easier with with ast because of the tools it has, especially the buffs. I rarely get comms as sch, but I get a lot with whm. Whenever I time holy just right and stun multiple aoe's so the group can stay together I seem to get major props.