I exported a video at the settings above and submitted it to Filmhub. It was rejected with the following (not too helpful) comment:
Overcompressed or Unsupported Codec - Video has a compression rate above Filmhub's maximum requirement, or was supplied with an unsupported video codec or file format.
but I can't figure out exactly how they relate to the output settings in Resolve. I don't see anything in Resolve's "Type" dropdown that looks like it would be any better than what I gave Filmhub already.
Any ideas what specific output settings might give them what they're looking for? They only let you submit three times before your film is ineligible, so a "throw you-know-what against the wall and see what sticks" approach won't work here
The maxed out quality settings might be overkill but I don't think that will be an issue. I'm even thinking it's possible that the reason the first one bounced isn't because of the compression but because it had a .mxf extension - though I can't be sure because their cryptic feedback that's in my OP doesn't spell it out. So I went with Quicktime and now it has a .mov extension.
Hopefully this one will do the job...we'll see what shakes.
So I've just been notified that the film has passed Filmhub's quality control with the above settings. As Uli pointed out, going with 10 bit instead of 12 would have most likely worked also.