Campbell
Relaxed Intensity
If the PCs usually operate as a group, ideally pooling their strengths and skills such that the whole ends up being a bit more than the sum of the parts, that sounds like a party from here. They might do different things in different ways than a typical D&D group might, but they're still a group. D&D's class system somewhat encourages this interdependence by giving each class specific strengths and weaknesses, though this has been watered down some in recent editions.
If the PCs generally travel etc. together but don't usually operate as a group then other than entirely-table-dependent in-character bonds of friendship etc. what keeps them together?
And if they operate entirely as individuals (which seems highly unlikely) then why have everyone at the same table each week?
In Apocalypse World the players play prominent members of a hard hold, a post-apocalyptic community that is scarce in resources. Almost all the action takes place within the confines of the hard hold. The community faces outside threats as well as internal strife. We're largely playing to find out if the player characters will pull together or tear each other down. It's the GM's job to frame situations that put the bonds within the community in doubt as well as to present external threats. One of the things you're supposed to do as a GM is to introduce NPCs that create conflicts of interest between player characters in order to put pressure on their bonds with one another.
It's largely up to the players how much they cooperate with one another. The type of scenarios you deal with are a lot more like Deadwood than they are like a typical D&D adventure.