Thats BS. Im 6'4" and 280 lbs and i ride just fine on it. Face it. with our body dimensions well never be pro riders but the YFZ will haul your ass around fairly well.
As for the size of the quad , i wouldnt worry to much, it feels small at first but once you ride it around that feeling goes away. Whats cool about being big is that you can really muscel that little quad around in the air.
Trust me, you will have fun with this quad. I am however looking to replace the stock coils on the shocks for heavier ones so i wont bottom them out to much when jumping.