For me this is a no brainer. Crew on main upwind. I usually sail single handed. Recently when I had the luxury of a nationals sailor to come out with me I crewed so I could check his style. Out on the trap with the main is awesome. No tiller to thing about and just pushing and pacing to power and using weight to best advantage.
I am absolutely clear that I would love it the other way round also. Just helming with a great automatic main trim.
This has to be fast so long a both people do their job well.
This also has the added advantage that the crew is going to be responsible for any harm he or she comes to and the main can be used to not 'fall" forward.
I bet that the control freaks have a great deal of trouble handing over the sheet thoug. I would suggest they would have more fun calling the shots from the foredeck.