Thanks jannik and Regis for your good answers. More than anything I think we've discussed different interpretations, I don't see much disagreement.
LEI's and single skins having obviously different construction than foil kites is IMO the main reason for different characteristics between them. Lot of single skin manners can been seen in strutless kites, but of course in any LEI. However small PA and heavier construction of usual LEI's limit low end.
It's ok if you Regis won't buy my interpretation or claim for correspondence between weight and drag. A bit paradoxically I feel like we've changed places: you have underlined the importance of low weight, I have said aerodynamic advantages are worth added weight. But because we have meant slightly different things for performance all this is understandable.
L/D can be increased by two way: having more lift or less drag (ok, third way: more D, even more L). Single skins use this third option because they tolerate so high AoA's before backstall and have very much bridle line drag. If you fly single skin kite through the window it first accelerates very fast but then reaches its flying speed which is limited by L/D. For high performance foil kite limiting factor is the size of the wind window (normal line lenght and windspeed).
So line drag is not very harmful for light wind performance. It limits upwind, high speeds and jumping ability though. LIft of a foil kite is limited differently and more than with a single skin, because if more lift is tried to achieve by adding camber it makes kite too unstable. Then also depower suffers a lot. AoA can not be increased because of backstall.
Thank you Horst Sergio
I agree with your opinions very much. Perhaps I'm having now a bit more active period for kites. All these new foils and also PanTau's wonderful work with LEI designs gives inspiration. I have some ideas, or combinations of used solutions developing or in process... If you or Regis or someone has a vision what could be useful or needed feel free to comment or suggest.