Theoretically…
…the Necky skeg can be adjusted to positions between full on and full off, but the controls really don’t allow it in practical terms. The pic at the link provided shows a rudder not the external skeg. The major problem with their skeg setup is that when “retracted”, it sticks straight out the back! It does not retract on-deck as the rudder does. This leaves the skeg vulnerable to getting bent - which renders it ineffective or worse - and creates a serious hazard when carrying the boat or loading it on a vehicle. It’s by far the worst skeg design I’ve ever seen. Stay away!
What difference does it make?
A boat that handles well in wind, handles well in wind. I’ve paddled in winds over 25 knots and had no need whatsoever for a rudder. It wasn’t exactly fun, but directional control was not a problem. High wind velocity does not make a rudder mandatory. Blanket statements like the one you made are invariably wrong and misleading.
It’s not even "technically correct"
High wind velocity does not make a rudder mandatory, regardless of rudder style. It may be mandatory on a suff ski or other racing boat, but it’s not mandatory on a well designed sea kayak.