Yes !!! I think the Captain has to arrange his breake so as to be in his seat for the tricky part of the flight
A colleague of mine brought a 744 back to Europe from South America on the very same night as AF447, on one of the parallel airways if I recall his account correctly. He had 10,000 plus on 744s, a South Atlantic regular and he reckoned that in his HO the sigmet chart showed the ITCZ was no "trickier" than normal.
So what are we defining as "tricky, and therefore captain must be in his/her seat weather"? Look at a Longhaul sigmet chart for, say, Asia and the subcontinent in the monsoon season...where's the "tricky part of the flight"? Probably starts at SIN maybe ends at Karachi, and then there's the "tricky" high ground and the "tricky" comms, around Kabul, oh and then after that the inevitable CBs (with associated severe turbulence of course) around Moscow or the Crimea and the dire warnings about being very careful if deviating in Russian airspace.."tricky" or not? Again a sigmet chart for the North Atlantic will quite often show that the NAT tracks are planned to pass through or very near to areas of forecast Moderate to Severe CAT..so by some definitions the whole of the Atlantic could be "tricky" on some nights.
If your are seriously going to mandate/insist that the Captain must be in his seat for the "tricky part" of every flight, irrespective of the qualifications and/or experience of the other pilots, how are you going to do it/pay for it? BTW I've no problems with two captains on a three pilot augmented crew if that's your answer
