Well, first of all we're interested in racquet "head" speed and its not just generated by the arm - far from it. Most lower level player use way too much arm in playing this sport and as a result either end up with arm/shoulder injuries, are totally inconsistent, can't generate much pace, etc. When just the arm is involved, there is excessive lateral movement into the ball as compared with rotation. When just lateral movement is involved the stroke is very sluggish and just won't hold up.
So, in my opinion, you have this a little bit backwards.