fWAR I think is much better than bbWAR for pitchers for sure - for hitters it is at least a little closer.
The bottom line is that Drew is a good shortstop, maybe better than that. But he is blocking a guy the franchise (and me) is bullish on. Could the Bogaerts-guys be wrong? Sure - no doubt. There is some risk there, but you make the best decision you can. Personally to me, the risk is minimal - 21 year olds who have progressed up the system the way he has, we are arguing between whether he will end up Jhonny Peralta or Alex Rodriguez (I know, I know) ... barring injury, it is extremely unlikely he is going to be a flameout. You want some depth? You don't spend on a true starter to provide insurance - or a supplement. Drew is too good to be an "extra guy" and the Red Sox would be spending too much money just to carry an "extra guy" of that caliber.