I don't agree with you that the wind range of boards are at best misleading or worse, deliberately wrong.
Some example. A 105 kg pal is using a Carve 162 + 52 cm stock fin + 9.5 sail in 12-18 knots of wind. I would be using such a combo in 7-12 knots of wind for my 65 kg; for 12-18 knots, I'm on a Kombat 86 + 30 cm fin + 6.9 sail.
Is the wind range of the Carve 162 above wrong ? Is it wrong to say that the Kombat 86 cannot be used by a 105 kg pal as of 12 knots of wind? Of course not... rider's weight does matter.
Just from the guesswork described above, one can estimate that a rider would need 1m2 of more sail surface for each 10 kg more of body weight.
Things get more complicated for a sinker : I need 20 knots of wind to get planing with an Acid 62 liters + 5.4 m2 sail but I strongly doubt it will be the same with my 105 kg pal. Is the wind range of Acid 62 wrong ? Of course not...BTW, Acid 62 rec sail starts at 4.7 m2, something certainly valuable for an average 75 kg rider but not necessarily true for a 65 kg rider.
Conclusion : wind range are an indication given for an average rider weight of 75 kg. My guess is that such a figure is the world average weight of a 30 years old male population according to some WHO (?) statistics. Average male weight is of course higher in USA (i.e., due to higher incidence of obesity) and lower in Thailand for example. Hence the choice of an average rider's weight to get a reference at some point in the big picture.
Would you have a better proposal as a rider's weight reference ? Why ?