It is my belief that your run-of-the-mill Bluegill will get to a pound pretty easily, if given a decent, perhaps even average environment, along with some supplemental basic feeding.(catfish feed). To push them to 1.5 lbs, then I think you need to step it up a notch, maybe by taking a more involved approach concerning water quality,(aeration) aquatic plant growth, fertilization to sustain natural forage, selective harvests, and a regular feeding program with a high quality feed. I think the 1.5 lb size is still attainable with an "average" fish.
Once we start talking Bluegills that are 2 lbs. or over, then I believe it might require an extra nudge, in the form of good genetics to push a quantity of fish over the top.
Now I'm just referring to maximum size potential. As Ken stated, I think there are many other factors and variables that lend themselves to having good genetics, such as rapid growth, resistance to diseases or infections, a high food-to-weight conversion ratio, etc.
