To use a bit of a metaphor, I kinda see a gravel bike like a rally car…..

You can have a formula 1 car (or indie car, if you want to keep things more “stateside”). They’re way faster and most compatible with the road - road bike.

You can have a 4x4 Land Rover (or Jeep, etc). They’re capable of going places off-road that pretty much no other vehicles can - MTB.

A rally car. A car that was ultimately designed for road use & still quick on road, but can also go quick on off-road courses. But not quite as off-road as a jeep can.