The only Me-109s that were good turners are the ones in simulators and in the minds of modern admirers of Nazi weaponry. Armchair "experts" who play aerial combat simulators and games look at one figure - wingloading. If they're relatively intelligent armchair experts, they'll also consider powerloading. However, the actual equations are quite complex. There are four factors which must be equally considered, not two. Lift, drag, thrust, and weight ... didn't anyone go to ground school?
Let's use the famous Me-109 versus P-38 argument. The 109 fanatics invariably say, "There's no way a 15,000 pound ship is going to turn with a 7,500 pound ship." But let's look at it a little closer. The Me-109 and P-38 both could pull 1800-2000 horsepower. I'll use 2000 horsepower for ease of calculations, though 1800 was a more common figure for both ships as neither usually were rated for 2000. Now, the P-38 has two engines, so that's 4000 horsepower compared to 2000. So we see here that the P-38 has twice the weight but also twice the power. Using just these figures, the sustained turn rates should be similar but the Me-109 should have a somewhat smaller turning circle because there is less inertia to overcome.
However, that's just half the story - weight and thrust. Now let's look at lift and drag. The Me-109 was a rather draggy design, especially the ones the unretractable tailwheels and larger cowling guns. The P-38, on the other hand, was so clean that it could get away from the pilot in a dive or split-S (this is aside from the early compressibilty). As for lift, the P-38 here had the better lifting wing by far. The P-38 had an 8:1 aspect ratio, whereas the Me-109 had a 6:1 aspect ratio. The P-38 had a thicker chord, too, which makes for more lift. Lastly, the P-38 had a superior taper ratio, being 3:1 as opposed to the Me-109's approximate 2:1. Add up these factors and the P-38 and Me-109 are very close indeed.
But there's one more thing. The P-38 had Fowler flaps. NACA (now NASA) tests show Fowler flaps to give approximately 30% more lift than conventional flaps, while having no increase in drag. With these flaps located nicely behind the twin Allisons, the P-38 enjoyed a considerable advantage over it's opponents. So while the Me-109, due to its lower weight and higher drag, was better in the instantaneous turn, the P-38 would soon catch up and then surpass the 109 in sustained turning. Me-109 aces advocated scissors when fighting 38s, noting that the P-38 was capable of "appreciably tighter turns" and "out-turned [the 109] with ease." The scissors, however, favored the Me-109's superior low-speed roll and instantaneous turn. The idea was to keep changing direction; the P-38 pilot could not follow for a short while, hampered as he was by his airplane's weight and inferior low-speed roll.
