I agree there's clearly an obsession with measurables - everyone wants that Randy Moss type who's 6'5 with sub-4.4 speed. But you see a LOT of big guys at WR that never amount to anything.
Size can be beneficial, it depends on the type of offense and the type of routes. If we construct routes specifically for Avery to take advantage of his speed and agility he will be very hard to contain. We need to use him in routes where he can go in and out of his cuts at blazing speed, catch it, then turn upfield, it's going to be very hard for any CB to follow him through one or two cuts without giving him a big cushion (look at his three cone drill times). I bet Saunders is excited and already has plays worked out specifically to use his quick moves to get rid of the coverage.
What I question isn't so much his size but just his ability as a receiver, running routes accurately, having that uncanny awareness of exactly where to be, having great hands, great timing etc. We'll see how that works out - we have a great coaching staff when it comes to WR so he may be able to improve more and faster at that than I think. I hope so.
For what it's worth, personally I believe the ideal size for a receiver is 6'0-6'1 and around 190-200 pounds. It seems to be the size of a lot of the top receivers (Marvin Harrison,
Torry Holt, Isaac Bruce, Chad Johnson etc.). The problem when you get taller receivers than that is sometimes speed, but even more often it's quickness and agility. A tall guy just has a much higher center of gravity making it much harder for him to make the mind-buggling moves that Steve Smith, Dante Hall etc. can put on a guy. I like a balanced WR somewhere between the huge jump-ball guy and the small nifty speedster.
Players like Moss are physical freaks, if one comes along sure draft him, but he's a generational talent physically - you are not going to see more than a couple of those players every decade (at the most) so you can't demand that every WR you draft is in that mold. If you try to go for that guy every year you are going to end up with a lot of Mike Williams (6'5, 230) type players. Ask the Lions how that worked out.