I can't grasp how people don't understand the difference between a flanker, a split end and a y. These days they are all lumped into the "reciever" category. There is a different job description for each position, and a different skill set for each one as well. Some positions, IE Flanker call for a long, speedy guy who has good ball skills and decent agility. Not spectacular agility, but the ability to make a hard cut on a dig or an out. They need to have good hands (not in the catching sense, but in getting off of jams and keeping their hands free from a defender playing catch-up) and they need to not stare at the ball. Others, namely the slot position call for a highly agile player with good toughness, great awareness and tremendous footwork. In my opinion, the slot is the hardest to play due to the multitude of responsibilities. They need to be able to crack down, they need to be able to run a screen, they need to be able to block safeties and wills/sams, they need to run the ball after the catch and they need to have the concentration to run through the hook to curl zone.
Welker, even with all of the admiration and praise that he gets is tremendously underrated. I have never seen a reciever with his footwork. I have never seen a reciever who runs with his pad level. It's so colloquial to lump all recievers together and compare who is best. The fact is, a z can't play y and vice versa. Z's get all the praise because they are long yardage and end-zone guys who make highlight catches and run 4.2's, but in terms of importance to the offense they don't outweigh the y. Welker is the best y in the league, arguably the best ever. He is also a top three player on the offense when Brady is in the game.