I wouldn't say "he hasn't progressed", however, I wouldn't say the the general hypothesis of the article is wholly wrong.
Dez is an incredible WR, however, for whatever reason he has lost of a lot of the escapability he had earlier in his career and his YAC has been going down. He isn't able to outrun people like he did earlier in his career and gets tackled from behind more and more.
Dez's yards per reception was 15.0 in 2012 and since dipped to 13.3 in 2013 and 13.1 so far in 2012.
I am knit-picking a elite WR in Dez, however, I no longer see the guy who was a threat to take a catch and take it the house on just about any play. I saw that in 2012.
Why? My working theory is his back issues, while not severe (as far as we know) have robbed him him of some of his upper gear.