See
https://www.diabetes.co.uk/diabetes_care/blood-sugar-level-ranges.html for NICE recommended ranges/levels.
I'm T2 and have kept my glucose at pre-diabetic levels eating a low carb/ketogenic diet from soon after diagnosis. I'm no longer on any diabetic meds. I initially set both my glucose meter and later my original Libre (when I was using it) to 5-7.5, and this is where
my glucose levels like to sit. My HbA1c is generally between 40 and 43, with occasionally higher blips usually due to other non-diabtic health issues, rather than diet..
And I agree that targets are personal. and I believe that type and severity of diabetes, and possibly other health issues, should be used to determine them. I also believe that we should allow for our targets being adjustable (up or down) if necessary and that probably time in target is what we need to work with.