They may be more effective, but not more efficient. Lowering the stall speed more doesn't mean they're more efficient. The drag is probably proportional, since the F-4U had conventional flaps. The P-38's Fowler flaps were more efficient; they greatly lowered the stall speed without greatly increasing drag. Even though the F-4U has a much lower stall speed with flaps, that doesn't mean its turn will be better. It will be tighter, but a lot slower because it doesn't have Fowlers. Moreover, the F-4U without flaps in game doesn't have a wide turn at all.
F4UDOA, how do you know that Dean's graph is wrong? And can you post corrections? Aside from that graph, I've seen another NACA graph comparing the F-4U, a few American airplanes, and the Spitfire. Once more the F-4U was on the outside. Unless you can convince me otherwise, I still believe that the F-4U has far too good of turning ability in the simulator.