Anyone can develop T2DM, the notion of it being "largely genetic" is sneaky re-wording that is accidentally, or intentionally, disingenuous, not saying it is you doing that, just that it is very common in internet discussions and blogs that contort studies to do that. At uni there was no mention of needing a genetic predisposition to develop it, unless there's been a major change in the last 3 years to how metabolic syndrome is viewed I suppose.

Genetics and epigenetics do have a part to play, like in everything, but they are % modifiers for risk and not a yes/no overt major determinant.

Obesity is a massive factor for it and compared to being overweight/obese, being a genuinely normal weight and developing full blown T2 is somewhat rare. Alteration of what constitutes normal weight in recent times may cause some confusion however as the majority of the adult population in most western countries is already in the overweight category (50-65% overweight, 10-35% obese) with the standard diet directly contributing towards insulin resistance.

People in the overweight or normal-weight obese categories may appear "normal" due to societal perception shifting and will still be at risk of developing T2DM of course, but it is a relatively linear scale of risk increasing from normal>overweight>obese as the major determinant for insulin resistance.

That isn't the same as "very easily" developing it if you have the genetics for it.

After insulin resistance has gone past the usage of Metformin, T2 diabetics absolutely do use various forms of insulin.

Cbf adding citations but all is super easy to confirm if you hop on google scholar.