Agreed that expectations should be explicitly stated. Takes the guess work out of the ride.
One of the weekday rides I do is a fast-paced ride, and it's understood that if you can't hang on they you ride solo for the rest of the ride. There is a brief stop at the halfway mark, so you have like maybe 10 minutes grace to catch up if you were dropped early. No one complains about it cuz that's what what the expectation is.