I ended up buying a Cervelo C3, advertised as an endurance bike suitable for gravel. It has Ultegra, disc, through axel, 28 tires with room for 32. My intent was using it for gravel and dirt trails but I now ride it almost completely as a road bike. It's comfortable on the road with the endurance geometry, good for gravel, and doesn't lose much over a road bike on fast riding.

Pretty much all the bike manufacturers make similar bikes to choose from.