Having been low carbing on and off (much more on than off!) for over 30 years now, my experience is that I feel great to wonderful on low carbs, and worse to dreadful on carbs. My cholesterol is slightly lower than average with optimal ratios. I eat a wide range of veg, enough protein, and get a good selection of nutritious fats. I eat a rainbow, enjoy salads and plenty of veg.
So that says it all, as far as I am concerned.
BUT there is a big difference between 'low carb' (less than 130 g carb a day) and keto (less than 50g carbs a day).
I am currently keto, and feeling better than ever. But is it sustainable for decades of great health? I simply do not know. Will feel the same in another 30+ years? Would I feel better, or worse than just 'low carb'? Who knows?
The only certainty I have is that eating 'standard carbs' as advised by most medical professionals will make me ill within a few days.
For me, large scale studies and general thinking is of no use whatsoever. They are aimed at most people. My body is more sensitive to carbs than most people. I get ill when I eat carbs. I get inflammation when I eat carbs. So generalised studies and research is never going to fit me.