Looks like Boston just won a title with Ray Allen??
I assume you know how silly that sounds (and yes, your simul-edit addressed that). At best the third most important piece there, and maybe even the 4th (Rondo). And they obviously hardly built around him. Its a poor example, but of course you aren't going to find many/any examples of building champions around shooters. We saw for a lot of years what building around Ray Allen does for you with half a decade of franchise killing suck up in Seattle -- and there they didn't just try to build around one pure scorer, they had TWO (Rashard Lewis). Next you can tell me how Orlando built their Finals run aorund Rashard Lewis.
No, pure scorer = good third amigo. But nothing more. They just aren't that valuable. They are like wide recievers in football. Add nothing at all without the great QB, bruising running game, and roleplaying offensive line. If they are your best guys, you are the Cincinatti Bengals. In fact by far the majority of championship teams int he last few decades haven't bothered to emply one at all -- they have gotten all the shooting they needed out of roleplayers who take care of business defensively and then hit shots when called upon rather than wasting time and capspace with soft little purebloods.