Your Hearthlings in groups stay on a similar schedule? Then maybe it’s a bug in my game. I’m seeing groups over time fall into a rotating schedule where at least 25% of the group is off doing something while the rest are following orders. Often I’ll have like one cleric by themself standing guard while the knights and archers sleep ;_; It’s terrible AI scheduling.
I have to disagree with #5, because I’ve played through late game. I always end up with a town that’s well-protected and has only one entrance, so enemies always come from a set direction. Town defense mode is only something I use in the first two months; by about 20 days in, I have a good combat group set up, and a month later, I have my killing maze built. (older post, but still accurate: Defensive designs ) The only time non-combat Hearthlings get hit after that point is when they’re out gathering resources from enemy camps and a war party of Orcs pops in and ganks them. 
I’d be OK with combat job Hearthlings not getting experience unless they’re in combat. I’d prefer that patrol and defend give similar exp, just because training is pretty helpful, but I’m right with you on the notion that you only get better at something by actually doing it.
Thanks for the reply and ideas. I’ll especially pay more attention to my farmers and their Body score. Thanks for that. 