My attention span was short, and I didn't get through all of this. Forgive if I repeat.
My horse is a pet, a tool, a partner, a friend. I hand walk him and my dog often (when it's too cold to ride). I go out in his pasture and play with him. I go out and just pet and coddle. I get on and gallop him in the dessert. I get on and jump a course with him. He loves it.
Keeping a horse happy means allowing him to do what he enjoys, get rewarded, and have some human companionship. I build trust in him with what I do. This allows me to gallop my OTTB around the desert sanely and trustfully.
BUT!! You can take being a pet too far. If you end up with a spoiled horse, you will end up with a horse you can't ride or compete with. He'll be taking advantage of you.
OR if you only use your horse as a tool, if he doesn't have the friendly human contact, or horse contact, I think you will also end up with a sour horse. One who weaves, paws, pins his ears, takes out his frustration on you...
There is a fine line between a pet, a tool, a friend, a partner. Those who can walk that fine line, raise horses who are the happiest.