Interesting question - but to the claim:
"From what people say, big boards suffer a lot with wind interference..."
I can say it is bull...
Yes, if you are ONE rider, having a small and a big board, of course above claim is correct - especially long huge beginnerboards.
But for two different weight riders? No.
Actually I would say heavier riders can have less wind interference than lighter riders, everything else being equal.
Say you have an average weight 75 kg and a "strong" rider 150 kg.
The big rider will use a bigger foilwing (but not twice as big) and a bigger wing (but not twice as big), and lets say they use a 75 and 150 litre board to match their weight.
Riding in the same wind, but the big rider with a lot more pressure on the board, and more power available, and a bigger wing - should "feel" wind interference the same way, if board "area" is doubled?
But it is not, a twice as big (volume) board is wider and thicker and a tad longer, thus not that much more area/drag.
So one could conclude the heavier rider will feel wind interference on the bigger board LESS than the light rider, one could claim
Just like he/she has less relative "body drag" because weighing twice as much, does not mean twice as much "body" area.
As with the board, "volume" increases a lot, but dimensions height x width x thickness only increases slightly.
It is not that simple I know, but in my eyes I can not see any reason why the bigger board should be a nuisance for heavy riders, on the contrary.
T.ex say we got a cube 5 cm on each side.
It has a volume of 5x5x5 = 125 cm3 and a total surface of 5x5x6 = 150 cm2.
A twice as "heavy" cube 250 cm3 would be 6.3 cm on each side, and surface area 238 cm2.
Meaning the 100 % heavier cube (body) will have 238/150 = 1.59 meaning 59 % more surface only, instead of 100 %.
If it was a sphere, it would be roughly the same, double volume (weight) only 57 % (Pi/2) more surface area.
Just to give you the idea and some food for thought, why I DONT think it is correct that a bigger board for a heavier rider is no good - just opposite in fact....
There are many other aspects and parameters in this so not that simple, but just to show my point
It is correct though, you need stiffer and stronger and bigger gear, yes, and some gear is not sufficiently strong for say 150 kg.
Peter