> Many active gym people have pretty high BMIs but fairly low fat

I think this is greatly exhaggerated.

Yeah you can put on as much muscle as Arnold and have a FFMI of about 27 then maybe have a BMI of 34 if you have 20% body fat.

But a very gifted natty might cap out at maybe 24 with a BMI of 30 at 20% bodyfat. But let's be realistic. This is not "many active gym people". This is the guy winning the local strongman meet.

Yes a couple of years training for most people can add a couple of points to BMI but I think people exaggerate how much this is. Go look at a 20lb brisket at costco - you don't see people with that much extra muscle all that often.