I believe that the dev overlay does not show the FPS doubling that frame generation produces. You need to use an external FPS monitor to show it.
This doesn’t sound possible. My 5800X3D and RTX 3080 with those settings (and lets be explicit here - 1440p, Ultra preset, AI traffic live, DX12, empty community folder) gets around 56 FPS at KLAX in the TBM.
Besides using an external FPS viewer to confirm frame generation is working, I’d also switch to TAA as your GPU is being under worked and you’ll get a much better image and about the same performance. Also try using DX11 and see if that improves things. Finally, try the high graphics preset, which is visually very similar to ultra but better performing.