Almost every trait, perk or feature can be used by these nasty PvP apes, I heard there are even BG sneakers. Let's leave that "argument", shall we?
For now Loner is useless as it is (to keep classic quote alive). To make it useful, we need to answer one important question - what solo player needs? Higher combat skill? Not much. Higher barter skill? Kinda. Higher "crafting" skills, to get rid of alts? Yes.
So in my not humble opinion Loner should work like a decent bonus for Science, Repair, Outdoorsman, maybe even Barter, maybe even ability to set a Ranger Camp without having a Ranger perk. I mean hell, you resign from having any in-game friends or gang mates, you can't join any group, you can't buy a base, you have to be self-sufficient Mad Max Wannabe wastelander, no alts required. That's real sacrifice in multiplayer game.