Have you tried it with FSR2 and DX12? I did with an rx 6650 xt and got a 4 to 9 fps increase for most scenarios in MSFS. The following link might be helpful as well:
Fps counters: external vs internal
Update hours later: An external fps counter indicates double the fps of the internal counter. Now I’m not sure what caused the 4 to 9 fps increase in the MSFS counter described above. The same increase was not seen when flying after a reboot.