in my opinion, the industry has converged. gravel geometry is road geometry, as regards fit. but we’ll see. just, if this isn’t it, then we’re telling ourselves a fairy story when we say gravel bikes can be ridden as road bikes or gravel bikes with a wheel and/or tire change.
Depends on what you mean by “road bike”. If you mean road racing bike…then yes, fantasy. If your “gravel bike” has modern road racing geometry and setup, then it’s going to be less than ideal in the more “difficult” off-road conditions. That said, I probably tend to treat mine as a bit of a “fully rigid XC MTB” more than most 
Then again, I also have my road setup with the bar tops a bit higher than most, and rely on deep drops in my bars to get the most aero road position…so, my positional setups between the 2 probably aren’t as great as others may have.
“Gravel” or “Adventure Bike” geometry and setup IMO should be more of a cross between old-school grand tour racing bike and a 80s/90s XC MTB…rather than a pure modern road geometry/setup. But, maybe that’s just me…