I've always had inside dogs -- even as a child decades ago, our GSD lived with the family.
My comparison point is the outside dogs who've come to live with me as foster dogs, and become inside dogs. Nearly all these former outside dogs had nasty coats with very gross skin underneath (often with infections or parasites), and medical issues the owners just "didn't notice," since the dog lived outside. We noticed them right away because in the house, our hands are often on the dog, massaging, petting, picking through fur, whatever.
My theory is that most dogs living outside just don't get the same level of care and attention that inside dogs get -- even when the owners mean well enough. Think about it: you know when there's any odd lump, bump, pimple, hot spot, foot boo boo, scrape, or anything else in your inside dog because you're constantly interacting and touching them. You know instantly when the dog is itchy because...thump, thump, thump next to the bed in the middle of the night. If that dog lived outside, your opportunities to pay attention or notice that stuff would be fewer. It thus makes sense to me that the inside dogs I see are in noticeably better health -- even the ones who come into rescue, we can almost tell right away when they were inside dogs, just by examining them.
Many of the outside dogs also come to us in rescue with storm phobia that seems to sometimes have a PTSD component, due to the weather patterns in our region. If they were left out in bad, bad tropical storms (and even hurricanes), they often tend to develop some residual reaction to the electrical fields that form when it storms. Some of them become absolutely terrified when lightening and thunder are happening, to the point of needing to be medicated. It makes me sad to think what it must have been like for them, alone in the dark outside while this stuff was going on. Even if they aren't naturally fearful dogs, there's often something weird about their reactions to rain or standing water -- one of them who became a housedog after living outside in a yard during a hurricane and several tropical storms decided she'd no longer step on wet grass again--ever. She would try to hold her bladder forever to keep from going outside and stepping on wetness. She simply hated it.
