Gravel vs non-gravel, I consider tow paths and rail trails to be different from all other types of gravel because towpaths and rail trails are usually reasonably flat and reasonably straight. Towpaths are almost always flat except where lock and dams are, rail trails rarely are steeper than 1.5 percent. Several times on a tour I took a rail trail over a paved highway because the paved highway had a lot more hills than the rail trail. And on a day with headwinds, often a towpath or rail trail will have more trees to block the wind. In this case, I obviously choose ease of pedaling over scenery or photo opportunities.

If scenery and photo opps are more important to you, then your priorities are different than mine, there is nothing wrong with that.

But gravel roads or mountain bike trails that were not rail trails or tow paths, these I would like to avoid compared to paved routes.

Some paved routes have more shoulder, and the routes where more money was spent to flatten the hills and raise the valleys are less hilly. But such roads are often busier too. Sometimes I prefer the flatter paved routes with more shoulder, but other times I take the rural roads that have minimal traffic, even if they are hillier. And the less used rural routes often have more dogs per mile that want to chase you.