as you say, the benefit of the “film” curve it to allow as much of the sensor’s dynamic range to be preserved and giving the colorist the flexibility in color correction.
Have you tried applying the BMD film LUT to the DNxHD footage? The fact that it is DNxHD footage should not affect color correction possibilities – especially if the original footage was ProRs 422.
You can still add a LUT to the transcoded DNxHD footage via source settings and will be applied on the fly. See if that makes a difference in resulting image quality. If it looks the same, then there may be issues with the exposure and other parameters of the file itself.
If you have Resolve istalled, then you can pull the .cube 3D LUT from its libary and import it into Media Composer to be applied. It will be called:
Blackmagic Cinema Camera Film to Rec709.cube
or
Blackmagic Cinema Camera Film to Rec709 v2.cube
On OSX, it can be found here:

Michael