@FarQM8 GW2 was spot-on! I haven't touched my settings there for years, so I can't remember what I've got, but I don't think I changed things much & they seem to suit all of my characters. In BFN I've found I need to fiddle around for a few different ones.
And I'm far from an expert but it seems to me that it's more than just aim assist that's a problem. Camera vs character movement definitely play a part, as I've slightly improved things by lowering look sensitivity (as well as aim sensitivity), but I still can't get it to feel as natural as GW2.