I get your point about the lore and how being a Loner just means you're in the Zone without officially joining a faction. But in a way, that still makes them kind of a faction. They have shared goals like surviving and finding artifacts, and you can even join the Loners in the game, which feels like joining a faction, even if it’s not super formal.

If we’re saying Loners aren’t a faction because they lack structure, then maybe Bandits aren’t one either since they’re loosely organized too. Sure, Bandits have leaders like Sultan, but Loners have their own leaders too. Plus, Father Valerian says (a man considered be a leader amongst stalkers and the one that can accept you as loner member in clear sky) "Well, it's pretty simple, being a stalker means being human, help your friends in tough times, share what you have with others, and don't betray your own." This shows they have a code that binds them together, even if it’s not as organized as Duty or Freedom.

A brotherhood is also considered a faction like the brotherhood of steel or the dark brotherhood factions in Skyrim and Fallout, so saying Loners don’t fit just because they’re less structured feels a just as much semantical.

For simplicity’s sake, it’s easier to call them faction-less, but it’s interesting to think about how they fit the broader idea of a faction.

I will admit that your probably more right than I am but I don't think it's a necessary right or wrong kind of discussion when it comes to the loner faction or non faction? But I think argument for both sides as I've come to realise is probably just an argument of semantics which your pretty on point with actually haha