It's a similar argument to the one going around the diabetes groups...does diabetes cause obesity or does obesity cause diabetes.
I wasn't even close to obese/morbidly obese until I hit my 40's. I had been overweight since I was 12. I am now overweight again by 5 lbs...but it doesn't explain my diabetes returning. My last A1C was 7.4 (my PCP doesn't seem to be concerned and has just told me to watch carbs, well, DUH!!!!!) But it had been creeping up for the last 3 years. Was 6.4 6 months ago. IF IT stays up thru the next one, I will ask to be put back on insulin. Can't go back on an insulin pump as Medicare won't pay for the pump for type 2's. But I have no fear of going back to insulin to help my blood sugars. I suspect my diabetes started when I was 30 since I had peripheral neuropathy symptoms that far back. I just didn't fail the FASTING glucose test until 1997.
Because of my pre-DS diabetes, I have been watching this. Diabetes relapses in about 4% DS patients after about 10 years. (Marceau 2015) (They defined cure as HbA1c <6.5 %). I don't know if the relapse rate keeps going up as time goes on, but it's saved me 11 years with diabetes even if it turns around now. Hope the next A1c turns around for you!