Having more catches is great, but Cruz is more versatile as he can, and does, operate on the outside as well as in the slot. The fact that "he got his bell rung" and never missed a game is in his favor.
Potential is what Cruz has far above whatever Welker has left. Welker turned down more $ to go to Denver. That indicates he's at the end of his career and he knows it. He wants to get to the Super Bowl