yea,,,, but then,,, if you were counting grams, the weight difference between a narrow tire and a fat tire is probably quite a bit greater than the difference between a narrow rim and a fat rim?

If you want to think this way, it's okay. I understand.
But nobody else, with any motorcycle (on-road or off-road!), any car, any truck, any tractor, or any airplane, or virtually anything else that uses pneumatic tires, will tell you that it's a good idea to use the narrowest wheels with the widest tires.
It may be technically possible, but it offers less-than-ideal performance.
Everyone else seems to understand that wider tires necessitate wider wheels. It is only with bicycles that this opinion is still shared.