PoE is an online game so you should think it is multiplayer.
But ingame its otherwise.
For example:
You must achieve youre mine depth in youre own mine.
You cant collect map stones in a party. Only the map owner can. that was true with shaper/elder parts as well in previous league's.
You must tick on shrines yourself to get that achiefment
and.. and .. and a lot more

The only difference between normal and sff is that you can trade stuff and level with others.
If you can find the right people because most interaction with others is a negative experience.