FWIW, I lowered my A1c from 9.something to 4.9 through diet and exercise, and have been there consistently since 2013. **What works for me** is a moderately low carb diet off the bike (25-30% carbs), and a normal diet before and/or during rides (40-60% carbs). On race day, I carb load like anyone else (lots of yogurt, fruit, gels, etc), but return to my regular diet after I've had a good recovery snack/meal.
I also dropped a lot of weight in the process, which contributed to my ability to maintain normal blood chemistry.
Assuming you are within your doctor's guidelines, there is a lot of trial and error to figuring out what works for your body and your exercise regimen. Be assured, however, that it is possible to reverse diabetes and get the on bike performance you would like. It'll just take some work.
BB
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Formerly fastest rider in the grupetto, currently slowest guy in the peloton
