Forceful is slighty stronger than Pounding with a Priest composition. The only disadvantage you have when using Forceful is during the beginning stages of a fight. Most of the time, Cable Step → Shadow is used as an opener to gap close and you would have to crit on Cable Step for your Forceful to activate, which is unlikely. If you do not crit on Cable Step, this means you are losing DPS on Shadow Burst due to the fact that Forceful was not activated. If you are using Forceful, I would suggest opening with Pendulum → Whipsaw.