If done properly the deep litter method is turning your coop or run into a compost pile.
I agree with everything you said except for the part about DLM composting in the coop. Composting requires moisture. The coop should be as dry as possible, especially in winter. A damp coop can cause problems for chickens like frostbite or respiratory ailments.
Deep litter is great in the coop but don't expect it to compost or generate heat. Fluff it up often over the winter to mix the poo in then do a complete clean out in spring. Use all of that litter to start a nice compost pile outside.