To be fair the beaufort scale is a measure of wind force.
knots, mph, kph, m/s all measuring speed.
Wind speed is only one portion of the triangle of air velocity, pressure and density.
Every wonder why 20 knots in winter feels more grunty than 20 knots in summer? Well its because the density of the air is more because the temperature is considerably less. Increase the air density will increase the force applied to the kite.
So... wind speed readings do not take into account any increase/decrease in force due to changing temperature/pressure. Beaufort scale does and therefore can be more accurate.
When WE measure the wind, we are actually assessing wind FORCE.
So arguing Beaufort vs Knots etc is moot. And it is irrelevant if we are measuring the wind in winter vs summer.
It is true that wind moving across the ground at 20 knots is denser in winter vs summer and therefore imparts more force. But we NEVER measure velocity across the ground. We measure the FORCE the wind imparts on the impellers of our measuring devices. Or we assess the wind strength by watching the force the wind imparts on trees, whitecaps, or other riders.
The Beaufort scale is less useful than other measurement scales for kitesurfing because it was designed for old sailing ships. Kitesurfers don't care about Beaufort 0-3, because we don't ride in these conditions. 95% of us ride in Beaufort 5-7. Also, part of the problem relates to the scale itself: The scale was designed in 5 knot increments. But wind generally becomes much gustier at stronger strengths. It is very rare to have 30k wind locked into a 5 knot range. More often than not, it covers 2-3 Beaufort ranges.