I know they were UFA. The point is that Bills cut them loose.
The "prime" of "Watkins, and arguably Dareus and Darby." was close to ****. Especially Watkins. The trade and decision to draft him was one of stupidest in Bills history...and there is a lot of competition for that before McBeane turned this franchise around from a laughingstock to a model to be emulated.
A reminder on just how awful the Watkins debacle was.
In 2014 the Bills sent the 9th overall in 2014 along with (inexplicably) 2015 1st and 4th round picks for the right to move up 5 spots to draft the porcelain doll Watkins. On the board when they picked Watkins at #4 were...
Khalil Mack
Mike Evans
Odell Beckham
Aaron Donald
Watkins NEVER started a whole 16 or 17 game season after his underwhelming rookie season. GM Doug Whaley made this ****ty move to try and salvage his other ****ty move the year before by panicking and reaching for EJ Manuel at #16 when he was more suited as a 3rd round project.
Ostensibly...or should I say....obstinately....desperately tried to prop up the crappy Manuel by giving him a
supposedly elite WR.
Watkins had elite speed and literately little else.
Whaley's record of drafts between 2013 and 2016 were terrible.
Beane traded away Watkins
and Darby (the other player you mention as being in his "prime") with those trades defining and transforming what the Bills would become.
Beane sent Watkins and a 2018 6th round pick to LA Rams in exchange for the Rams 2018 2nd round pick and EJ Gaines. He sent Darby to Philly for a 3rd round pick and WR Jordan Matthews.
With extra day 2 picks in his pocket, it set up Beane to do all the maneuvering to move up in 2018 to draft Josh Allen. After trading Gordy Glenn and the Bills 2018 #21 (and a 2018 5th round) to Cincy for 2018 #12 overall (and their 2018 6th).
To get to #7 overall to get Allen, Beane sent the #12 (from the Cincy deal) #53 and
#56 they got in the Watkins deal, to make the best draft pick of the Bills in decades.
In addition, Beane used the pick he got for Darby to draft Harrison Philips.
Getting rid of Watkins and Darby (in their "prime") and letting Gilmore and Woods walk were just what the Bills needed.