So many ways to go here. Obviously calories play a role, but I highly doubt adding 50 grams of intra carbs is what you need. I've brought my back up a lot in the last 2-3 years so here are some thoughts.
Most guys' biggest issue with back is poor mind-muscle connection - namely, they row with their arms instead of their back musculature. All the rows in the world won't do shit if you don't actually feel the lats squeeze and stretch through the movement. Don't row with your arms - focus on your elbows being the hooks that pull your arms backwards as your lats contract. Let your elbows guide the movements.
There are no required exercises for back, or any other muscle group. I brought my back up without doing a single floor deadlift, barbell row, dumbbell row, or pullup, because I simply don't feel those exercises well in my lats. My favorite back movements are Hammer Strength plate-loaded low rows; pulldowns on a Free Motion double stack with adjustable arm height and width; and Smith machine rack deadlifts - these have done more for my back thickness and density than any other movement. Don't follow the dogmatic bullshit, figure out what exercises you feel and make progress on them each week.
If you have long arms you really need to find your appropriate range of motion on back exercises - it isn't pulling back / down as far as your arms can go. Practice movements with no weight to figure out what your back's ROM really is, then start adding the weight.
Single arm movements are great for a better mind-muscle connection and ROM, and very useful for guys with long arms. Rack deadlifts are the only back movement I do with both arms, everything else is one arm at a time.
My back has made the most progress using 8 - 12 reps. On rare occasions I may go 6 on rack deadlifts, but that's it.
Splitting back into thickness and width days definitely helped me. The increased training frequency will help hypertrophy and being able to do half the work on a day you're not deadlifting and greatly fatiguing yourself can also help. I generally do 12 sets on my thickness day and 11 on my width day.