a tip for your back double biceps. Try to flare out your lats more. It will show way more back width if you do that!
Further, I think your erectors are in proportion to your mid, upper back development. Very good.
You got a nice back there, good job.
Exercises that helped me a lot to develop that lower-back section (but also the full 3D look a back):
- Deadlifts (heavy, low reps)
- Rack pulls (heavy, low reps)
On those 2 exercises I would focus on form and simply moving weights. Those exercises are also very good for overall back development, huge deadlifts will also build good traps, rhomboids, lats etc. Not only erectors.
For general lat development, exercises such as:
- Pull ups
I always tried to focus more on form and muscle connection and really squeeze the shoulderblader together at the top of rows, pull the dumbbell or bar from your elbows and NEVER forget to squeeze the shoulderbladers at the top of the movement. That last part will help develop your rhomboids and together with big lats and good developed rear delts. That will give you that full upper-back look, combine that with your good erectors from your deadlifts and erectors and you got a very solid back.