I basically assume it'll be subpar. And more often than not it is. It isn't uncommon to have a good player in your party. Pretty rare to get a full party of good players. It doesn't make things any less fun for me, it's just something I noticed.

The only exception is when I'm an early starter (right after a patch hits) people who get through the content fast tend to be experienced players. If you made it to 80 on day 2 you essentially spent your time sharing party with people who had cleared ultimate fights and knew the game and their classes well. It's often like that, the first few hour clear parties for anything are usually pretty decent. Everything goes downhill from there.