Agree, you will always be a bit less efficient, or a lot, toeside when going upwind.
The very best riders are so good that they can get close, where beginners are very far, and us mere mortals are somewhere in between.
It has partly been discussed in this thread I remember:
Timing when carving
This "inefficiency" is why we can not carve as well toe-to-heelside in light wind, as heel-to-toeside, flying the kite normally over.
As you need to go reasonably high upwind before carving, to have a chance in marginal wind.
Also the reason why it is usually way easier to downloop, to carve back from toeside in marginal winds, as here you can carve first and keep the lines tensioned thus more chance for success.
Whereas with heel-to-toeside carves you can start going higher upwind at same speed, so you can fly the kite up and over without getting slack lines thus possible to make a flying carve in marginal winds, as opposed to toeside to heelside turns.
I often carve flying the kite up from heel to toeside, and then "cheat" and downloop when carving back from toeside - in marginal winds, as it works.
But I also KNOW it is my personal inefficiency upwind on toeside that is the very reason why I can not carve back in marginal winds, so I practice flying the kite up first, eventhough I have to give up sometimes and downloop instead
PF