4 wheeled boards create more friction than 2 wheeled boards. I understand the weight distribution on two wheels as opposed to four, but that is more valid for rider-only, not rider plus kite which is much more force. When the board slides out, you have 4 tires moving laterally through the grass, as opposed to two. Plus, the kite force creates much more force than body weight, alone. Looking at a two wheeled design, the rider+kiteforce is distributed through your feet, where the moment arm is above the board and only slightly behind the tires as you edge with your heels. Very little force is being driven down. For a 4 wheeled board, two wheels are in front of the feet toward the kite, and two are heel-side. When you lean back, with the CG if front of the heel-side wheels, those wheels are driven into the ground, creating much more friction between the board and the ground.
Conversely, if you're being pulled over the board and you push with your toe-side, the 4 wheeled board gives you a larger moment arm to get board grip with the toe-side tires (like the "wider is better" pontiac commercials)
I can see great benefit from a two wheeled board for long grass, where there is too much friction from 4 wheels preventing you from riding, but I can't justify buying a board like that for one situation. It seems to me that 4 wheels work better for short grass, dirt, snow/grass, sand, soft sand, etc...