There have been dozens of wide receivers on the Patriots since 2000.
How many of them has Brady made into good receivers?
Why has not Brady made all of them into good receivers?
There is zero credence to the argument to Welker being a product of Brady. He excelled with Cassel, and he was productive with Miami - productive enough for Belichick to see he would thrive here.
No one gets open like Wes Welker, and anyone who says he won't be productive elsewhere is nuts.
That said, if your point is that Brady isn't making receivers better, I have to disagree there. Name me a receiver who has gone on to have more success outside of New England than in. Gaffney is maybe the only one, and that's in large part to him rescuing his career as a Patriot.
Branch, Patten, Givens, Caldwell. Heck, we get a minute from a Super Bowl with Reche as our top receiver and he only starts one more game in the rest of his NFL career. Sam Aiken had 330 yards in our offense and never plays receiver again in his life. Doug Gabriel was out of the league soon after the Pats moved on, Chad Jackson too. Bethel never did anything. Ocho and Galloway were busts, but they were obviously toast, too, both soon out of the league themselves.
The guys who have failed in the Patriots system haven't done jack elsewhere. They either sucked or were out of gas.