Well, ours are stalled at night especially in winter, but even now because I think it's the only time my old Bay will lay down at night. So from observing him, I think he sleeps better and is more alert in the daytime when he's been in. We're in Western WA, and I don't think long periods out in wet are good for them. They come in just to dry off at night.
BUT, they go out to pasture every day, rain or shine. This is more important because we don't ride as often as we should, and they move and run quite a bit playing with each other.
I think horses being turned out is a must. I wish I could turn mine out more then I do. But if I turned them out 24/7 they would get NO grass. They are not ever "stalled" but kept in smaller runs when not out on what pasture I have. Usually about 1/2 the day they get to get out of their runs.
It will be easier when Belle goes back to her pasture.
Becky