I'm not super familiar with SF construction materials but I wonder if that plays a part in it too? If your neighbors are separated by concrete walls then you're probably getting less interference from them than you'd think and your mesh might actually work better(?)... but what do I know since I'm no networking engineer.
Old Victorians in SF will sometimes have lathe and plaster walls (the 'wet wall' that drywall replaced). Lathe and plaster walls often have chicken wire in them that degrade wifi more than regular drywall will.
