But is the Mustang less structurally strong? Also, escorting bombers and fighting in the 20-30,000 foot band is right in the Mustangs wheelhouse, not so much for the Thunderbolt.
Also much is always said of the twin engine P-38 for safety, I hate to spill it but you're not there to be safe, you're there to find, fight and kill the enemy, the P-38 is an excellent platform, but when the chips are down and my ass is on the line, I'd take the higher performance of the Mustang any day of the week.
Hell, they flew 8 hour flights from Iwo to the Empire and back and I don't see Mustangs just dropping into the Pacific because they only have one engine or aren't "rugged" enough. I could be wrong but here's a pretty good site about long range ops from Iwo
506th Fighter Group Home: 506th Fighter Group, 457 Fighter Squadron, 458 Fighter Squadron, 462 Fighter Squadron Iwo To Japan
Also, not trying to sound like a dick so please don't take it as an attack, just a different point of view.