I don't know if a 5'8" 175 pound WR is ever going to have the volume or durability to dominate in the NFL
Certainly a valid concern. But it's worth pointing out that DeSean Jackson has at 5'10" 175.
Yea, there's a precedent, but up until this season Jackson had never really been a featured WR. His career high in receptions after five seasons was 62 catches. They also have very different playing styles, with Jackson historically being more of an outside deep threat and Austin being more of a joker.
not much smaller than Welker
He's actually a lot smaller than Welker. People don't realize how stocky Welker is:
Welker - 5'8.75" 195 (29.0 BMI)
Austin - 5'8.5" 174 (26.1 BMI)
To put those numbers into perspective, Welker's height/weight ratio is greater than Vincent Jackson, Dez Bryant, and Larry Fitzgerald. A typical big WR will be right around 27.5-29. Anything over that is more in line with what you usually see from a TE or a RB. Austin's 26.1 would be right near the bottom of the scale if you were to look at successful receivers in the league right now. DeSean Jackson is quite a bit smaller with a 24.4. AJ Green is down near the bottom at 25.9 (though he's 6'3"+ to help compensate). It's probably worth noting that those guys are used primarily as outside receivers running downfield, so they're likely not as exposed to violent hits across the middle as someone like Welker. That isn't Austin's game at all. He's more of a slot weapon than a conventional outside WR.
If you look at the FF-relevant players in that role, you get a pretty short list of Harvin, Cobb, and Welker. With a 21 pound advantage at basically the same exact height, you can see how Welker is a bad comparison from a physique standpoint. Harvin and Cobb are a little better. At 5'10.25" and 192 pounds, Cobb has a 27.4 BMI. At 5'11.125" 192 pounds, Harvin has a 26.7 BMI. A few things stand out to me here. The first is that, despite having only moderately higher BMI figures, both of those guys are almost 20 pounds heavier than Austin. The second is that both of those guys have already suffered some serious injuries. While it's too early to tell the story of their careers, it's possible that their thin frames combined with their usage as hit magnets over the middle will result in long term durability issues. I'd also point out that while BMI tells you a lot about a player's body type, "bigger" is still better in the sense that a taller version of the same body type will usually have more strength and power (i.e. Darren Sproles vs. Steven Jackson/Adrian Peterson -- Sproles is actually "thicker" from a BMI standpoint). That doesn't bode well for someone who's both thin and really short like Austin.
Add it all up and I think you've got to question the conventional wisdom that Austin is well-equipped to handle a high volume slot role. I rated him pretty high out of college because of his draft slot and speed, but I also urged caution because of how atypical his game was. This scouting report from CFN last year really struck a chord with me and I think might be the most accurate take on his skill set:
7. Tavon Austin, West Virginia 5-9, 175 Proj. 2
Positives: Fast, fast, fast, fast, FAST. Great with the ball in his hands in a variety of ways and is always able to come up with a big burst of speed whenever he gets the chance. … A great runner in an open field with the potential to become a special slot receiver. He’s going to be uncoverable at times. … Always producing. He doesn’t need a lot of room to make one cut and fly.
Negatives: Size is going to be a problem. He was able to get by in college, but he won’t be able to take a licking at the next level going across the middle. … He’ll be used as a kick and punt returner, but his future will be as a receiver. He needs to work on becoming a full-time wideout, and while he could be a difference maker, it’ll be as a fun toy to play with. … He’ll be limited in what he can do for a passing game. He’s strictly an inside target.
Really, What’s He Going To Do In The NFL? He’ll be a flash of lightning who’ll take over a game or two on his own. However, he’s not going to be a superstar receiver who’ll make ten grabs a game.