It distracted it, which is sometimes all we need. It was big and flashy and allowed us to set up the combo. If Abel didn't shoot it with lightning Gren would have a much harder time setting up his attack. As you've mentioned a long time ago, Abel is best for tanking. Gren has some CC and Mobility, but they're all revolved around either getting into a fight or keeping the enemy from getting away from him, and no way to actually defend himself like with Abel's electrical barrier. Eating bullets is not a viable means to distracting your opponent.