While Bears and CoB excel in this situation, PB suffers from its inability to hit over a large area and to attack in more than one direction.
If you have used PB for any length of time, the AI always seems to attack in the same way e.g. the main attack comes from the front and then the monsters circle you to hit you from the sides and back. Much like the AI used by fire-chained elites.
My old approach for dealing with this was to hold down the PB button and move the mouse left or right to spin my character, which results in more of a pin wheel application of PB. While the pin wheel attack would get the job done, it doesn't feel very efficient and if fact it makes me long to put bears back on the skill bar.
After playing in a dungeon it finally hit me on how to best use PB. To fight monster groups, always put your back to a wall. The best situation is a wall that obstructs the monsters and makes them come at you from one direction.
However, any wall will do, as you have now confined the monsters to 180 degrees of attack instead of 360. So instead of a pin wheel approach, you now can hose the monsters from side to side and don't have to deal with monsters coming behind you. It may sound like a simple idea, but I find PB is much more effective with a confined area of attack.
Another technique I find helpful is using Horrify/Frightening Aspect (plus armor) with PB. After the monsters interrupt your PB casting, when they are beating too hard on you, you are low on mana, they surround you, or they have just thrown too much hoo-doo down where you are standing -- these are the situations when I use Horrify.
The fear from Horrify clears the monsters away from you, it doubles your armor, and puts you back in control of the situation (so you can move to another wall and get ready for them when they come back). Also, many of the monsters will die from the PB DoT as they run away, so it is a win-win to use Horrify with PB. Horrify will also break fire-chained elites apart, and works on all elites no matter their size.
That's all I have for now. Feel free to share what you do.