The P-38 I would say was the plane that if it was introduced earlier, wasn’t hamstrung politically or restricted in engine performance could have change things earlier, the first prototype crashed and was destroyed, the ones sent to England were not as powerful as the original concept, same old story like the Warthog, it was a deviation in tradition and was not liked.
There were reports that it may have been the first to actually have broken the sound barrier in a power dive.
Late or not, the P-38 shot down more Japanese aircraft than any other USAAF fighter in WW II.
Now, I am taling air-superiority “fighter” here. There are other planes, with other missions, but this thread starts with “fighter.”
Speed was up to 426 m.p.h., and best climb to 3,900 ft./min. The “J” would climb to 20,000 ft. in 5.9 minutes.
Nothing else came close.
IIRC, the initial Lightnings delivered to the Brits had no superchargers and lacked counterrotating props. I think that the Brits shipped them off to secondary theaters because the just couldn’t compete at high altitudes. The lack of counterrotating props would tend toward handling problems.
The P-38 was great against Zeros but not good in a dive and had lousy engines.