Golden Tate has never had a 1000 yard season, but there’s an argument to be made that he’s a better wide receiver than Eric Decker. His numbers have been kept down by a run heavy offense, but he’s averaged 1.80 and 2.01 yards per route run in 2012 and 2013 respectively. Compare that to 1.80 and 2.03 for Eric Decker and they’re much more comparable than you think. Golden Tate also had a better 2011 season, when he was a 2nd year receiver with problems at the quarterback position, than Decker did in 2011, when he also was a 2nd year receiver with problems at the quarterback position. Golden Tate averaged 1.33 yards per route run, as opposed to 1.28 yards per route run for Decker.
Now take into account that Eric Decker has 29 drops compared to 216 catches (1 drop every 7.45 catches), while Golden Tate has 5 drops compared to 144 catches (1 drop every 28.8 catches) and that, as good as Russell Wilson is, Golden Tate was playing with the inferior passing quarterback between the two. Eric Decker got 36.25 million over 5 years (with 15 million over 2 years guaranteed), while Golden Tate got 31 million over 5 years (with 13.25 million over 2 years guaranteed), which is more reasonable.
Tate moves from one of the run heaviest offenses in the NFL to one of the pass heaviest in Detroit and Matt Stafford isn’t really a downgrade from Russell Wilson as a pure passing quarterback. He’ll have an opportunity to run 600 pass routes opposite Calvin Johnson, see single coverage with regularity, and get his first 1000 yard season. The pass heavy Lions were incredibly thin at wide receiver after Calvin Johnson and were able to upgrade their passing attack tremendously with this move. It’s a reasonable value and a good use of the Lions’ limited cap space.