Flight Time: Do you really think the upwind ability is an issue on most modern kites? I cannot even remember the last time I thought oh I wish this kite would go upwind a little better. It is a given, and it still has nothing to do with actually riding the wave to do.
IMO the kite means almost nothing at all, compared to other factors, regarding upwind ability - the difference will not be noticeable really.
But the BOARD is essential - and you need a board that goes upwind well, as it is not really the kite that matters much, but the board makes a huge difference in upwind ability.
Size, rockerline, tailkick, edges etc etc.
Fortunately, most dont want too slow boards today (like earlier years where kitepower was used more), so they actually go upwind quite well - even if we just choose our preferred waveboard without thinking of upwind ability
Even the most low AR kites today, go upwind easy IMO
So no, I dont agree that upwind ability is important whatsoever, in wavekitedesign.
But I agree that upwind ability in general, is one of the really important parameters, one of the top on the list.
It is the board though, and not the kite IMO, that makes by far the most difference here