No situation - especially this one - should be allowed to drag a team down in this way. Technically is was the right thing to do, and it ensured the migration went well.

In my view the problem here is motivation. It is as much the manager's or team leader's responsibility to maintain morale as it is to manage timescales, cost and quality, and it sounds like they were sleeping on the job 🙂 All it needed was perspective, encouragement and a positive "can do" attitude.