I like light bikes too and looked at a used Cannondale SuperX recently but someone else scooped it.

My current gravel bike is an old Trek XO2, it's aluminum, has rim brakes, rides and handles like a road bike, and comes in at about 18lbs with pedals and bottle cages. I can get 40mm tires on it which isn't ideal but I'm not too bothered by the couple mm I'm missing.