Type 2 question about non overweight Type 2 diabetes

I believe I have a pretty low personal threshold for visceral fat accumulation before developing IR and BG dysregulation. I had a history of quitting smoking, putting on 20kgs and ending up pre-diabetic. This happened once in my late 30s, again in my late 40s. Third time lucky in my late 50s I ended up with a diagnosis of Type 2. As soon as I'd start smoking again, I'd lose the weight and return to apparently normal BG. I imagine there was still some level of IR going on (apparently smoking causes IR all by itself), but enough to restore normal fasting BG. I've no doubt I still had bad post-prandial reactions to challenge meals, just like I still have today, despite being normal weight but that was never tested. I also know from genetic testing that I have a cluster of SNPs related to risk of developing Type 2, especially one relating to lower insulin release.

This time I managed to lose the weight without taking up smoking again - best decision I've ever made. I really wish the internet had been around the first time I developed pre-diabetes, but hard to know if it would really have made a difference.

Sometimes diabetes, is a consequence of a genetic predisposition, and not related to weight.
People of South Asian , African, Afro- Caribbean, Non European origin Hispanics, Polynesians, Torres Strait Islanders, Maoris, and other Pacific Islanders, have a lot of diabetics, who have no weight problem.
They have a liver which churns out more glucose than their muscles can take up, the constantly elevated BG, leads to excess insulin sloshing around their system, subsequently resulting in IR, then T2DM.

As for me, I've been a smoker for forty years, when I vaped for 14 months my weight did not change. I am also caucasian, of Irish and Ulster Scots background as far as I know.

I have my own musings on TOFI-ism or MONW (Metabolically Obese Normal Weight) but I have nothing with which to back this up. I am in favour of Prof. Taylor's hypothesis of PFT (Personal Fat Threshold) which ties in nicely with the possible genetic predisposition hypothesis.

I learned from Giles Yeo that there are 200 genes associated with obesity, some of these genes are switches and some could be described as dials. Although Yeo's lecture was on obesity rather than on Diabetes it seems to me that these dials must be a key element in why some of us are metabolically obese at a much earlier stage than others but until more research into the possible (probable) genetic element is carried out we shan't be any the wiser.

To be honest, I would prefer research to start off with a view to developing cheap, accurate testing to warn people earlier of the risk of rising IR or eventually a genetic test though as lifestyle wrt the modern western diet plays its part I'm not sure how this would actually play out.

There are things that I am absolutely convinced about. Insulin is probably one of the most powerful hormones in the body, one of its roles is that it drives fat storage so it follows that hyperinsulinaemia drives weight gain. Calories imo are irrelevant. It seemes logical therefore that as we are all unique my level of IR is intrinsically linked genetically to the insulin response my body has to food.

Edited to add.

I mustn't forget about Glucagon. When compared to insulin, much less is known about glucagon and it is possible that this antagonist plays a much more important role than may previously have been thought. It could turn out to be the ugly duckling in all of this, who knows?
It was only a few days ago that I found out that one could be glucagon resistant.