Clearly some people overrate him and others underrate him, he is a bit of an oddity in the NV and can be hard to judge. As for his techniques, I think his Earth Grudge most closely falls into the category of 'forbidden jutsu' rather than KKG as there is no mention of it being related to his family.
Certainly his use of fire and wind is not a KKG, nor would I even call it a pseudo KKG. Why you ask? Because simply combining the elements is not a KKG, rather its the altering of the 2 elements to become a new element. Wood is a perfect example. If Kakuzu fired water and earth at you at the same time would you call it wood? No wood has unique properties and is a completely new element. Kakuzu's use of Fire and Wind only seems like a pseudo KKG because Fire and Wind simply do not form a clear new element like Water and Earth does.
So no, Kakuzu is simply fanning his flames with wind, not creating Scorch.