Kane..a suggestion for the hypertrophy work on rows plus lower back endurance.
Personally I think deloaded rows abslulutely suck for "lower back" and there are so many more direct and efficient means to get that.
I would highly recommend after doing your primary set switch to another row with support so that you can focus on the upper back rather than trying to kill two birds with one stone...which is a noble idea but not always the most productive, imho.
Then just do more core work. Planks, side planks (and various variations of those
), pallof press and other anti-rotation.
Remember that a big part of what we think of as lower back endurance is also abdominal endurance and stability. Basically trunk stability. And the rows really hardly engage the "stiffness" in this complete way.
There are lots of other things to do but I'll leave it at that for now.