The world record was caught in a special environment that was even unique for Alabama. Even there the state record was 2lbs 8oz. prior to the discovery of large bluegill in Keytona lake. Conjecture there was the reason they got that large was because the chemical makeup of the water enhanced longevity and that there wasn't a large population of mature adult bluegills to compete with for food.
The Second Best Bluegill
The state records for the adjacent states Georgia (3-5) and Mississippi (3-7) aren't even within a pound. Only two other state records even exceed 4lbs.
5 of the 49 states show new state records since 2000 with those in CA and AZ starting to creep into world record territory just as they have taken the recent records for readear sunfish. That being said, there haven't been any recent records in the southeast. Unlike you though, I think other factors such as changes in agricultural practices, lake fertility, and trophy bass management have as much or more to do with that than changes in harvest patterns. Yes, bigger bluegill can be bred just the same as is being done with work on bass and whitetail genetics, and if that is your thing then go for it. As for me, I cannot tell a difference in the overall bluegill fishery now at the age of 50 than I experienced in 1970. Different waters have been more productive over the years with some being consistent and some coming and going, but overall not noticeably different.