Common sense is not so common......
No, physics knowledge is not very common. Friction between two surfaces doesn't depend of the force applied between them. So the fact that a torque is transmitted or not trough the driveline is irrelevant.
What happens in a 4x4 TC is that the axles are rigidly locked. Therefore any small, even tiny, difference in axles rpm's (due to multitude of factors) will lead to some binding between axles and the clutches inside TC will start to spin - and THAT will reduce the power with the small amount described above. 4x4 TC will dissipate the heat made by internal friction clutches when rpm's are perfectly identical.
The AWD is a true differential, hence this reasoning is NOT applying. If rpm's are slightly different, they will NOT increase the friction significantly. Only on high levels of delta rpm the VC will 'lock up' and even then only partially.
You cannot deduct that, because the 4x4 binds slightly on asphalt, the same thing will apply to the AWD.
Same thing for people comparing some farm equipment to the AWD differential - is the same thing. You are not comparing apples to apples.
As I said before, nobody here made any real MEASUREMENTS of the gas mileage. Only Ford did, for factory setup, but those are different engine sizes.
I even proposed a simple 'free rolling' test (to support my statements), but that is too complicated for some. They will rather apply 'common sense' judgments and have no clue that they are wrong.
Common sense is dangerous - that convinced people that Earth is flat or that the Sun is rotating around Earth.