As I did note, eating comes first.
That being said, when my dad was doing chemical marketing research, he investigated cat foods on one of his projects. They told him cats would eat sawdust if it had the right fats on it. So the fact a cat is eating it may just mean they've got the right flavor enhancers on it, not that it is particularly nutritious.
And dry food is just that - dry. I've had several cats over the years with renal disease, before I knew about the long-term impact of dry foods on many, if not most, cats. It was heartbreaking to watch them be slowly poisoned by their body's inability to remove toxins (and they need more water to do it, the worse the kidneys become), become more and more uremic (you can smell the urine on their breath when they are end stage), losing weight, starting to vomit because of the uremia, and when they stopped eating, having to euthanize them.
Renal disease is a known complication of diabetes; anything you can do to reduce that risk is worth it. Please Keep working on the wet or raw foods trials, following the transitioning ideas from Dr Pierson's site.
At least learning how to do subcutaneous insulin injections partially trains you to do subcutaneous fluid injections. should you ever need them (dehydration can occur from numerous conditions including DKA, hyperthyroidism, renal disease, diarrhea, vomiting, and more)