I am FB friends with friends; people I know through DD's school; family; old school friends; parents of old school friends if I was close with them at the time; old colleauges; people I know through my hobbies/social activities.
I only have around 50 or so friends so might only have a couple in some of these categories.
I'm naturally closer to some of these people than others. There are a couple I'd stop and have a light chat with, there are some I'd say hello to if I passed them, there is one I don't even really say hello to.
But then I think I've got a pretty good grip on what FB is for and how different people use it. I understand that people use it in different ways to me - my News Feed evidences that!
I tend to think of a frenemy as someone who appears superficially to be a friend on the surface but then seeks to use their closeness to you to undermine you and cause problems for you in your life. I would describe the people you describe as just disinterested tbh!
I'm always surprised that people have so many problems with FB, tbh. It is what it is. I've never had to defriend someone, I've never had an argument with someone on FB, I've had to delete a couple of my mum's posts on my wall, but tbf, she's my riskiest FB friend! 
I think people take FB waaaaay to seriously!