I have read numerous times, from varouis sources, that the Lightning had a terribly cold cockpit so I don't think it is anything but true. I think the "gripes" about the P-38 performance are relative to where they were deployed, how used, what they faced, and what type of other allied fighters were available or also in theatre.
That being said, from what little I know of that theatre that encounters were not numerous. We know the P-38 out performed most Japanese planes anyhow so there would be little to gripe about. And I don't recall reading about anything other than P39's and P-40's being used in theatre, so the P-38 was "it". No Mustangs, Spits, or Thunderbolts to compare to in that area of the war.