Yes Kew, of course there are genetic factors, there always are, but diet is a huge factor... As with many endocrine disorders, the interaction between genes and environment is so complex that it's hard to tell if (for an individual) dietary modification will help a little, a lot or not at all. But it's worth trying surely? Costs little and will do no harm.
For many people a high carb diet (in conjunction with their genetics), is the cause of the insulin resistance that lies at the root of many health problems. As a society we are profoundly metabolically disordered. Pcos may be a marker for underlying metabolic disorder rather than a cause of metabolic disorder... Without a high carb, processed western diet, those people wouldn't have got sick in the first place, regardless of their genes.
Drugs like Metformin to lower blood sugar have a role to play but they are a sticking plaster, and all drugs have side effects. Surely better try and see if diet modification works for an individual (it might not, but it might work better than a drug regime).
Although I do realise my crazy views go very much against the "call everything a disease and sell them a pill, in fact sell them lots of pills" ethos prevalent in modern health care 
!!!