It can not be good for the transfer case to run with the front wheels stopped for any significant amount of time.
There is no bearing or bushing on the pinion gears and the pinion shaft in the center differential, just metal on metal.
They are not designed to spin at high speed for long periods of time.
I have seen the pinion gear and shaft gall and sieze in rear differentials where the driver was spinning a tire for a long period of time in a futile effort to get out of a stick.
You are right.
And the centre diff spins much faster then the front or rear and is smaller.
This is why the centre diff locks automatically in low range, and also why there are warning stickers stating to lock the centre diff (if you have the button from factory) when there is a chance of wheel slippage.