Dogs don't know how to do nothing. They're really bad at it and they need our help at making them feel like it is a comfortable option. Let's be real, left to their own devices dogs will make really, really crappy decisions. Even if they are well trained, in the absence of the owner they can make really poor choices. Most dogs do not know how to self soothe in any way. Crate training, place command and obedience commands with duration, teach dogs to control their impulses, regulate their adrenaline, and feel comfortable doing nothing... even when the world around them is doing all kinds of stuff.
Duration work is not something you do all day every day. That would be pretty boring and really unfair. It's a skill just like any other that should be practiced, but not over-used.
Milling around the house is a pet peeve of mine and falls into the category of the rehearsed behavior of a dog that does not know how to relax. Milling does not lead to chilling. Tether training is a wonderful option to teach a dog to self soothe that does not involve any actual commands. Tie your dog up to a strong fixture in your house and go about your morning or evening routine. Expect that there will be protest or tantrums. Never leave the house or go upstairs to take a shower with a dog tethered. You don't need to keep constant eyes on the dog, but you need to be there to check in. Turn on the radio and do the dishes. When your dog stops fussing and actually lays down to rest, go ahead and release him. Rinse and repeat and you will have a dog that knows how to self soothe within seconds and actually enjoys doing so.