EVERY gun has a use, its simply about selecting the best gun/ammo combination for any job.
We don't always take out the .308, most of the time the jobs need something a lot smaller. When I first started doing the supermarket/shop birds I used the FAC air, around 28ft lb, soon stopped that as even with the pigeons the shot commonly went clean trough and left holes in walls, so the lower power certainly has a use.
What ft lb is your FX running at and what type/weight of pellet do you use? Fixed target distance is a general indication of rifle/pellet accuracy and 120 yards is a lon