The question is not 2 or 4. It is 4 or 5 or 6
As a minimum if you are camping/cooking/carying food etc then you need two rear panniers, a tent bag or sleeping bag bag, or a dry bag.
Plus you need a handlebar bag, you need somwhere to keep the days map so you can see it without the need to stop at every intersection and get out the map, plus you keep the camera, the money, the passport etc there. That bag NEVER leaves your side (or front)
The other set up is to loose the tent bag or sleeping bag bag, or a dry bag. and swap it for two small front panniers, which is probably the preferable set up
PS - Carry the tent poles on the underside of the top tube held on with a bungee. Carry the fuel on the underside of the down tube in a bottle cage