I agree with this. I went to a mini tennis camp this weekend and and the pro told me to "just use the arm", don't worry about the body. This is kind of the opposite of the advice you normally hear - but for some reason this clicked with me. This only makes sense in the context though - I already had a decent unit turn and preparation for the shot, I was just "muscling" the swing too much, trying to get the whole body into the swing. This really hampers my recovery, takes a lot of energy, and actually makes the swing slower.
Having your whole arm fairly loose from the shoulder down will result in a whip-like swing with lots of power (and spin if you use a sufficiently vertical swing), assuming you have the good preparation, which it looks like the OP does. You can initiate the swing with the body/hip, but it seems like the body actually needs to move very little to generate a very fast/powerful swing.
Just my latest observations... Maybe I'll change my mind tomorrow