There were 66 wide receivers with salary cap hits of at least $2,000,000 in 2017, based on data from Over The Cap. There were 67 wide receivers in 2017 who had at least 700 Adjusted Catch Yards, which is receiving yards with a 20-yard bonus for touchdowns and a 5-yard bonus for catches (for reference, Jeremy Maclin with a 40-440-3 line is the cutoff here at exactly 700 ACY). In other words, I wanted to set a bar for both salary cap hits and production that was pretty low, but not so low that the data would be overpopulated with fringe players.
There were 89 wide receivers who had either cap hits of $2M or 700 ACY in 2017. The correlation coefficient between the two variables was 0.31, indicating a moderately positive correlation but nothing more. The graph below shows those wide receivers with salary cap dollars (in millions) on the Y-Axis, and Adjusted Catch Yards on the X-Axis. The most valuable receivers would be on the bottom right (low cap hit, high production) while the least valuable would be on the upper left (high cap hit, low production).

The five at the bottom right are Michael Thomas, Tyreek Hill, Jarvis Landry, Adam Thielen, and Brandin Cooks — all but Thielen had a cap hit below $2M, with Thielen being the dot at $4M but with 1,812 ACY.
On the other side, in a world of his own, is Tavon Austin. With a cap hit of nearly $15M, Austin was the fourth most expensive wide receiver in 2017. He finished the season with just 14 receptions for 61 yards and zero touchdowns.
Here’s another way to think of it. For this group of 89 wide receivers, the average salary was $4.86M, with a standard deviation of $4.29M. So Thomas, with a cap hit of $1.16M, was 0.86 standard deviations below average in terms of salary. The average ACY was 977 with a standard deviation of 517. So Thomas, with 1,865 ACY, was 1.72 standard deviations above average. So Thomas had a Z-Score of -0.86 for salary cap value and a Z-score of +1.72 for production. If we subtract cap hit from production, Thomas has a value of +2.58, the best in the NFL last year. Austin, with Z-Scores of +2.36 for salary cap and -1.64 for production, is at -3.99 in terms of value, by far the worst in the NFL.
What stands out to you?