This rests on management for hammering gate agents and FA's with on time departure nonsense. If you leave 5 minutes late but take care of you passengers, the pilots can more often than not make that time up.

Now, I don't know when the seats were offered. Were they offered right as he boarded or was he already in the back of the plane and the isle chair already gone? If it could have been done in a reasonable amount of time, it should have been done. If you were all buttoned up and ready to go, I'm sorry but the time to do it was 10 minutes ago.

I wouldn't be quick to throw the FA's under the bus as they are taking their orders from people who only look at performance numbers and aren't out there day to day taking care of and dealing with the passengers and probably fear they will be disciplined for taking a delay.