The critical point in speed management when carving is to fully complete your turns, meaning you carve past the fall line and back uphill before transitioning to your next carve. You need a fairly wide slope for that but it's the way to go if you want to slow down and prevent excessive speed.
As far as boards go, I can't answer as I didn't try a WWW, but if I understood correctly, it's more of a jib board, meaning it is optimised for short turns and can loose both edge grip and stability when trying to make full C-shape turns. The fact it's pretty soft flex doesn't necessarily imply it won't carve, because if you manage carefully your speed, you can stay at a speed where this flex is enough to hold an edge, but it certainly would wash out if you begin to gather too much speed. The real problem I guess is more that the board will want to return all that flexing energy to your legs long before you have completed the turn, making it harder to keep carving past the fall line.
Generally, good carving boards are a bit more stiff than that longitundinally and have a pretty stiff tortional flex in the nose and tail as well, in order to help the edge grip the snow on its full length. Yes I would say that a board designed for carving makes it wayyyy easier, but the riders technique is far more important than the board.