Agree with trying to work in more volume. It's a volume game for sure. I do a similar approach to improve my back. Trained it 4 days per week, 4 exercises, 3 sets per exercise, 15 reps per set, last set always to failure. It worked is all I can say. It worked enough that I'm still doing it (8 months later), and now my back is my best bodypart. It'll never be Yates' back, because I have a long torso, but I'm doing the best I can with what I have. Day one: horizontal pulling (all kinds of rows...machines, dumbells, bbells, whatever...)Day two: trap work (shrugs, high pulls, power cleans, power snatches)Day three: lower back (reverse hypers, deads with bars or DBs, hypers, etc...)Day four: vertical pulling (chins, pullups, pulldowns, 1 arm pulldowns, pullovers)I would do this, and in between sets for back, super-set some other bodypart. Day five I worked arms on their own, because it's just real hard to do biceps supersetted with a back day. And legs were never a problem, so I trained them like a twink while I gassed out on back.I'm waiting for my elbows to wear out or tear a biceps, but it hasn't happened. Knock on wood. I think it's because I use pretty light weights versus you monsters on here, and really try to focus on mind-muscle connection. Most guys with weak bodyparts will admit their mind-to-muscle connection sucks. So I always think that's a good place to start. If your back is weak, you should work to be able to (someday) just stand there, contract your lats, and make them cramp up. That's mind-to-muscle...not really scientific, just something important I think.
