Agree, it is impossible to compare foil wings, as every parameter is important.
Even volume is not a measure of lift/drag at all, as camber and LE rounding means a lot more.
Apart from, as said, AR and sweep.
So the more numbers available, the better, and Gong is quite good at this, compared to many other brands.
But riding the wings, are only way to find out how it rides
My question though, was solely, how other brands measure surface area:
1. Projected area.
2. Flat area if no dihedral.
3. Upper surface area.
4. "Felt" area.
As Gong writes the Felt area as the number on their wings.
Peter