Comparing Claypool to the potential of a hypothetical 2nd round WR, there have been 32 WRs taken in the 2nd round over the last 5 drafts:
Claypool is 10th out of 32 in yards per game, and 6th out of 32 in touchdowns per game. So he's solidly in the top 1/3rd of WRs drafted in that round over the last 5 years.
When comparing to just the last 3 drafts (since they'd want somebody to be productive for Fields ASAP), only Tee Higgins (33rd overall pick in Claypool's draft) has more touchdowns per game, with Claypool well above the 17 other 2nd round receivers in that time.
So the odds are firmly against finding a better WR than Claypool with that pick, and even more so when looking for one that can contribute more to Fields's continued development in his third season.