Re: the social aspect.
Apart from my battle against the Norwegian family, I had another run-in last weekend. A slot opened up in a Mystic gym in this park, so I jog on over there, only to find its prestige already falling. I look all around for possible culprits, and see only a little kid - like maybe 8 years old, tops - sitting with his parents, eyed glued to his phone. Once the parents got up and pulled him along, the damage stopped, and I resumed training. Just as I manage to pop my Flareon in there, this gaggle of shirtless bros wander up, all talking about being on Valor. I was completely outgunned, but I kept training anyway. I giggled like a child as they complained like "wtf why isn't the prestige falling further" and for some reason it never occurred to them to look around them. They won in the end, but not without frustration.
I'm beginning to understand that trying to defend a gym alone against a group is futile. So my solitary player strategy is pretty much just training up existing Mystic gyms, opening a slot, and popping one of mine in there, however briefly.
Also noticed another tendency about gyms (in my area anyway): high flow of traffic past the gym = greater turnover, while a higher flow of traffic to the gym = higher level gyms. Like, a gym at a busy downtown intersection will be at Level 3 and change hands every few minutes, while a gym at a concert hall will be at Level 7 and be held by one team for several days. Makes sense as I think about it; it just never occurred to me before.