I don't lay any blame on Allison. Allison made what the Air Corps wanted .(funded). I believe the Air Corps dictated low to medium altitude performance, thus a single stage integral supercharger on the base Allison. To get performance at altitude, they wanted the Turbo, which did work well too. But they gutted the Turbo installation from the Airacobra and I believe the Warhawk too. At the times these aircraft were designed / delivered, the Air Corps still believed the Heavy bomber needed no escort. They fought through that belief all the way into 1942 if I recall.