I'm fortunate enough to live in a county with 1 (one) stoplight and more gravel roads than paved roads. Gravel bikes are at home here. No traffic and friction between drivers/cyclist, and no off camber wet roots to ditch over on a mtb.
For me the fun of the gravel bike frame is that you really can come up with a unique ride/build. Mine is a trek 930 I found in a garbage can, mounted 700c rims, and as much road stuff as possible. It has a campagnolo record bb with a 102mm spacing for roadie q-factor, and ultra low gearing for climbing some steep grades.
I always chuckle at myself when people talk about disk brakes and like to think my v-brakes are essentially disk brakes with 700c rotors that weight less, but I understand that a lot of people are getting disk. Seems like every road bike these days has a set. Not me though. Even in the mountains, I still am not burning out rims, and wet weather braking has never been a real issue. If I was building a road bike, I would go all CF like 171 said, but for gravel, or touring, I would consider a steel framed "one off" build in a heartbeat.
Gravel bikes slow? Here's one video on road. I thought it was with my road bike, but then I saw myself going after potholes. I will upload some more gravel bike goodness soon.
another-
https://youtu.be/FoX0X5enBoM
and another-
