I would say the P38 realy could shine in the pacific, simply cause the extreme speed advantage over most japanese planes.
It was somewhat like the 262 in 1945.
In Europe it dont had more to offer than the german planes. The Speed was similar(depending to the altitude), it had a relative bad initial roll, up to the J the roll ratio at highspeed also wasnt good and its dive problems are also well known.
But all this dont mean it was bad. The missing torque, the good upzoom (not climb, the constant climb wasnt outstanding, it only was the best US climber in 1941-44, the good upzoom is related to the big inertia at highspeed), the dive acceleration, the range, the firepower and good manouverability at medium to highspeed gave the pilot some possibilitys to get a kill and to survive.
At the end the performence of the P38(specialy J and L), same count for the 110, 410, P51 and P47(specialy late D´s) depends much to the current fuelload, this planes must have had very big differents in dogfight performence from take off to landing due to this.
So once more it depends to the pilot(and team), the tactical need and the tactical situation when the fight start, if the plane is successful or not.
In the ETO the Spit(great interceptor) and P51(great escorter) could do all needed things better(at least the german pilots had more respect for them) and it was more cheap, so the P38 got replaced.
Greetings,
Knegel