I'm serious though. It was far easier to produce Mustangs. In what was a war of attrition, numbers matter. Top production output for a month on the 38 was 402. Top for the 51 was 857. And it took less men to crew a 51 then a 38. I'm a 38 guy, but if I'm running the war and know I can put 450 extra fighters up if I go with 51s, I'm going with 51s.
I think the 38L took the idea as far as it was going to go too
I think the F7F Tigercat is proof the idea didn't go away. But Jets showed up and props were obsolete
No, the P-38K took the idea almost as far as it could go. Eventually, the G series Allison and a four blade Hamilton Standard prop would have maxed it out. The G series Allison might have even made it possible to lose the turbocharger and the attending complexity, given the fact that it could have been fitted with a two speed two stage crank driven centrifugal supercharger. How much Lockheed could have done about compression we'll never know.
Had Consolidated Vultee of Nashville been building B-17's instead of doing a poor job of trying to build P-38's, as opposed to having Lockheed build B-17's on what should have been the other half of P-38 production, the P-38 production could have been doubled, and more updates/upgrades been phased in. There's your 800 P-38's in a month. Almost like being second sourced, as the P-51 actually was.
However, nothing would make up for the cost and complexity of the P-38, or the logistics required, including maintenance. Nothing except rock solid performance, and there, other than absolute top speed, and dive speed, the P-38 shined brightly. The P-38K might have been near dominant in categories other than dive speed, and been close even in top speed in level flight, although it would have been at or near compression speeds. No single plane was at the top in every category, but the P-38L was pretty high in all of them, and the P-38K would have been far superior.
Perhaps the ultimate proof the idea didn't go away would be the P/F-82 Twin Mustang, which was in fact Allison powered.