i am pretty inclusive of maneuvers when i think of a maneuverable, pretty much anything that can be considered a maneuver across the entire envelope of the aircraft. i include up, down, right, left, speed up, slow down, roll this way, that way, and back, all considered at all sorts of speeds.
flat turn, yo yo, lag roll, 1/2 cuban, split-s, etc.
so i tend to consider much more than how tight a plane can turn near it's stall speed when i evaluate a planes maneuverability. this approach to evaluation of a planes maneuverability comes from talking to fighter pilots about how they evaluate a plane.
i think we differ in this regard, and it is at the root of some of our disagreements.
not a bash, just noting that i think we have a different outlook.
EVERYBODY who flew both types and compared them in r/l considered the 38 the superior "dogfighter".
The 38 has a high-aspect ratio wing, large fowler flaps, and a superior power-loading as compared the P-51. All of this still does not give it a turn *radius* superiority over the Mustang, but it does give it a healthy advantage in sustained turn rate. Furthermore, its torqueless design will always be far easier to fly right to the ragged edge than any single-engine prop job. All of which is in turn unimportant in a P-51 vs P-38 fight compared to what the 38's advantage in the vertical gives it.
Basic wingloading will often give you a guess, but its not always accurate. Comparing power-off stall speeds in various configurations is the easiest sure way to find the true ratio of lift/weight.