Best healing games are healing stalemate games where the fights go on forever.
Priest had AA. My monk friend was the real top healer there, IMO. The horde priest did a ton of healing as well. 
https://cdn.discordapp.com/attachments/698960631788994710/1106425959109890109/AA_healer.jpg
Damage will also be very high in this type of game. Alliance KBs are much higher because Horde only had 20 players for a large part of the start of the match (probably queue-syncers not taking the queue because enough of them didn’t get in together), then backfilled with some more solid horde players that stalemated the game.