I had type2 at 6yrs old so your theory for me doesn't work, for me. However I'm morbidly obese. I've fought my weight, all my life. I did have a diabetic burn out a few years ago and I weighed more as my bgs were out of control. However, not much more thou than uncontrolled diabetes even with insulin. Mixed insulin got me losing weight when using high volumes. Separate insulin isn't as stable, for me.
Body size and bg control are NOT related. I can control my bgs whatever size I am.
Ok I need more insulin the more fat I carry. So yes, more insulin resistant but no more than that.
I can trick my body into behaving better but it's a very heavy intense management. Eating a certain way but not calorie deficient reliant.
Diabetes is about the whole of your body not just pancreas! And definitely not fat.