Yup, Boomkins really make this trivial. Pre-shrooming an add has it slowed by the time it's up, and Typhoon will knock back as many as you need on one side. You can pretty much have a Boomie assigned to any three adds (probably farthest three) and just have DPS and tanks worry about the rest until they're down.
That being said, we run with 2 boomies in our 10-man (yup, weird, I know) and what we do is always assign them to the adds spawning on either side of stairs, have tanks + 1 melee running to side where hammer drops (since they have better stuns for our comp) and other DPS handle rest. For hammer in middle, we have me (Resto Druid) and our HPally stun the adds closest to stairs and rest of DPS get other adds to 50% before nuking those.
There really is no "best" strat though. It's just about DPS knowing how long it takes them to get an add to 50% before moving on to another one and then telling the RL what they're comfortable with. We took 5-6 pulls on that phase to figure out how to do it. I personally hate assigning specific numbers on the adds, but RLs from other guilds I'm friendly with swear by it. It really depends on your DPS. Post-nerf, telling them to just use common sense is totally fine as long as they're using their class correctly on that phase.