Exercises Per Upper Body Workout - Fatigue

Have done as few as 3 with intensification/failure methods (while having some left in the tank), and as many as 10-12 with straight sets. But this is utterly irrelevant.

I think you are in much need of some metabolic conditioning. Have you looked into Thibbs’ Metcon for Muscle plan? I think you would do incredibly well with this, meeting multiple goals and targetting some weaknesses.