I think it changes every year but this year is a unique situation itself. Scoring is way up and offensive production is way up so far this year.
Still waiting for PFR to update the last 4 games but right now teams are averaging 25.4 points per game (this was at 27 or so after 4 weeks, its gone down a bit) right now. For the previous 3 seasons this average has been 22.4 now as more games are played I would expect this average to continue to go down towards the average, but right now all teams are scoring 3 more points than average.
A lot of the extra yardage is coming from the passing game so WR as a whole are doing more than usual. Or maybe this becomes the new normal as these numbers do seem to keep going up a bit over time.
One of the main contributors to offensive improvement has been the lack of offensive penalties compared to previous seasons..
The rookie WR draft class of 2020 does seem to be living up to the hype. I don't remember this many rookie WR being relevant right away since 2014 and even that great group took a bit of time to get going like OBJ. I will wait for more data but it should be interesting to compare the 2020 group to the 2014 group at the end of the year.
Here is the top 50 WR by total points and PPG in the second column
1. Ridley, Calvin ATL WR 121.00 20.167
2. Hopkins, DeAndre ARI WR 119.10 19.850
3. Thielen, Adam MIN WR 119.00 19.833
4. Diggs, Stefon BUF WR 115.50 19.250
5. Cooper, Amari DAL WR 110.10 18.350
6. Anderson, Robby CAR WR 104.90 17.483
7. Jefferson, Justin MIN WR 101.70 16.950
8. Metcalf, DK SEA WR 101.60 20.320
9. Robinson, Allen CHI WR 99.30 16.550
10. Lamb, CeeDee DAL WR 99.00 16.500
11. Hill, Tyreek KCC WR 98.80 16.467
12. Fuller, Will HOU WR 97.50 16.250
13. Woods, Robert LAR WR 91.50 15.250
14. McLaurin, Terry WAS WR 91.00 15.167
15. Claypool, Chase PIT WR 88.60 17.720
16. Lockett, Tyler SEA WR 88.20 17.640
17. Boyd, Tyler CIN WR 87.50 14.583
18. Evans, Mike TBB WR 87.10 14.517
19. Beckham, Odell CLE WR 86.82 14.470
20. Slayton, Darius NYG WR 83.30 13.883
21. Kupp, Cooper LAR WR 82.10 13.683
22. Allen, Keenan LAC WR 81.60 16.320
23. Cole, Keelan JAC WR 81.40 13.567
24. Moore, D.J. CAR WR 80.40 13.400
25. Crowder, Jamison NYJ WR 79.30 19.825
26. Parker, DeVante MIA WR 77.40 12.900
27. Beasley, Cole BUF WR 75.80 12.633
28. Cooks, Brandin HOU WR 75.70 12.617
29. Jones, Julio ATL WR 70.00 17.500
30. Brown, Marquise BAL WR 69.70 11.617
31. Chark, D.J. JAC WR 69.50 13.900
32. Higgins, Tee CIN WR 69.40 11.567
33. Sanders, Emmanuel NOS WR 68.40 13.680
34. Shenault, Laviska JAC WR 65.40 10.900
35. Fulgham, Travis PHI WR 64.40 21.467
36. Landry, Jarvis CLE WR 63.38 10.563
37. Patrick, Tim DEN WR 63.00 12.600
38. Smith-Schuster, JuJu PIT WR 62.40 12.480
39. Gallup, Michael DAL WR 62.10 10.350
40. Cobb, Randall HOU WR 61.70 10.283
41. Adams, Davante GBP WR 60.30 20.100
42. Gage, Russell ATL WR 59.70 9.950
43. Ward, Greg PHI WR 56.50 9.417
44. Watkins, Sammy KCC WR 55.50 11.100
45. Aiyuk, Brandon SFO WR 55.40 11.080
46. Kirk, Christian ARI WR 55.30 11.060
47. Williams, Preston MIA WR 55.30 9.217
48. Edelman, Julian NEP WR 53.92 10.784
49. Humphries, Adam TEN WR 53.00 13.250
50. Brown, A.J. TEN WR 52.70 17.567
There are a lot of 2nd and 3rd year players on this list as well so there is somewhat of a changing of the guard as you say (and this continues) as there are only a handful of guys producing at a high level who are not from this younger crowd.
As far as buy low sell high I think you want to buy rookies who haven't performed yet but you believe in for example for me Jalen Reagor. It is the worst possible time to buy a rookie when they are performing well like Jefferson. Maybe Aikuk can still be had for a reasonable price. Amari Cooper is a sell because I think Lamb ends up being more targeted than him in time. It depends on what you can get for him or other older guys like Thielen right now. Usually folks wont pay what they are worth once they get older, and for good reason. I end up keeping or even buying these players because no one will give me enough for them.