Doug,these SGL's down here are below 11 DPSM with plenty of understory.Matter of fact the greenbriar is so thick alot of places you can't even bow hunt.Simple it's overhunted.
Here's where I disagree with you.I know a few areas that held lots of deer yet had great oak regen in the sun.My woods by camp were basically ferns until I opened the canopy.Now thick as can be with various regen including oaks and wildflowers.A mere 25 feet away in the shade nothing but ferns.Ferns love shade.