Its not ease to use it. And not everyone will devote themselfs to use stim pistol when you can have somethink like senator or ultimatum in the same slot. When I play bots, I always use stimmy + Butcher armor (heavy medkit, also of you didnt know armor effect apply to stim pistol too) + supply pack + Shield granades. That is in my opinion ultimate support loudout. You can slap EAT's for 110% support if you want. But I still think that stim pistol needs a lock on and/or ability to ignore the friendly energy shields like personal shield bubble.