Jake Shields was once the dominant Strikeforce middleweight champion, but those days are long gone. In the UFC, he's just another fighter and it's due to his style.
Shields is a good fighter but he doesn't match up well with the other members of the welterweight elite.
The American Jiu-Jitsu founder has good wrestling and great Jiu-Jitsu, but his striking is still robotic, awkward and lacking power.
This doesn't bode well for Shields, since contenders like Rick Story and Johnny Hendricks are practically tailor made for such a style.
They, too, have a wrestling background—which will enable them to stuff Shield's takedowns—but their striking is far more polished and powerful.
Shields vs. either of those two would be a replay of his fight against Jake Ellenberger: a one-sided beatdown.
Even other welterweight fighters like Diego Sanchez and Rory Macdonald are bad stylistic matches for Shields. They can nullify any of his wrestling and then just beat him up on the feet.
In the age of true mixed martial artists, Shields is still fighting from the early-mid 2000s era where being a master of one area of fighting while being merely proficient at the others was enough. In the modern era, Shields' days are numbered if he doesn't evolve.
A move to middleweight might temporarily "save" his career since he can use his wrestling against the division's numerous strikers, but eventually his lack of striking will catch up with him; It's change or die in the UFC and Shield's hasn't changed much.