There can sometimes be a middle path. I once had a flight that experienced delays which would mean exercising discretion to fly the sector back to base. My FO was chirpy (his sector) but the Chief Purser told me that one of the junior girls was mildly unwell and unfit to operate. The rest of the crew were all fine. No problem. With 14 CC (happy days of yore) we had enough crew to operate legally up to several juniors light, after all, we were a top airline with full service. The unfit CC deadheaded back and everybody was happy.