I'm the only T2 currently and have been diagnosed for just over a year, but, my Mum was T2 (now deceased) and I have suspicions about my late father's metabolic health too, because he always used to say that if he went more than a few hours without eating he felt faint.
My brother and sister are both overweight with a big tummy so they may also be heading the way of T2. We have all struggled with weight since our late teens/early twenties. (sister's husband is T2, diagnosed some years before me but he follows the ' NHS pills are handling it' route
).
My own thoughts on the genetic vs food argument is that it's both for T2's.
Genetics comes first I think with the type and number of our genetic markers giving us a predisposition to be carb. intolerant at varying levels, so we spend longer or shorter times developing metabolic syndrome/insulin resistance and getting to diagnosis.
Diet plays in after that, and the 'eat carbs not fat' guidelines of the recent years are triggering massive upswings in problems.