You may need to read my sentence again a little more carefully: Me 410 convergence lockup is fixed under Patch 9.
Now for the "DX9" versus "DX11" on the splash screen, what I did was installed Patch 9, said "Yes" to start AH3 now, and the opining splash screen said "DX9". Check to see if the convergence button for the Me 410 was working (it was) and quit. Started the game later and splash screen was back to "DX11". So the DX9/DX11 thing only happened "within" the patch installation process.