If grip is limiting your workout, you should do as much as you possibly can until you need the straps. There's nothing inherently wrong with using straps to strengthen your back if your grip has given and your back has more to give. Try Liquid chalk, Fat Gripz, pinch holding plates, dead hangs/ holds at the end of reps and if you havent yet, think about switching to hook grip which is the strongest grip, but will most likely start as the weakest.