cannot turn as well at that speed with a P-38, especially a P-38L which can deploy its dive flaps to aid in a high speed turn.
People in this game have a habit of claiming that "x" plane turns better at high speed. And in every case it is nonsense, and a pet peeve of mine.
An aircraft's turn performance above corner speed is limited by G tolerance. The only other limitation that may come into play is if heavy controls disallow the pilot from pulling as many Gs as he can stand. And every "pilot" in the AHII skies is limited to the exact same 6 Gs. 400mph IAS is well above corner speed for both the 38 and 190.
Aircraft types DO NOT MATTER. If two planes are going the same speed and pulling the same number of Gs (let us say the 6 Gs that we are limited to in AHII), then their turn rates and radii are EXACTLY the same, not better or worse. This is an immutable law of physics. Furthermore, any speed in excess of corner velocity decreases turn rate and increases turn radius, so the initial advantage in any turning starting out at 400mph or so IAS would go to the pilot who decelerates his plane more quickly to corner velocity.