Running dog
Much of what you say is true but outside the training environment most people descend with some power in a cruise descend rather than a glide, this keeps the engine temp more stable and makes the practice of warming the engine unnecessary.
I also think that the "keeping dust out of the engine" thing that the training industry is so keen on is a myth unless you operate in a desert environment, the path for the air when carb heat is selected is such that in a normal northern European environment not a lot of rubbish will enter the inlet track.