Here is the mean absolute deviation of the percent usage rate of the top 10 pokemon used in each ou meta. A higher MAD implies higher overcentralization, lower means more even usage/more variety.
gen 8: 5.7484
gen 7: 5.0548
gen 6: 3.34125
gen 5: 5.1617
gen 4: 13.561
gen 3: 9.5912
gen 2: 21.512
gen 1: 24.768
source:
https://www.pikalytics.com/ 