PS: In short, it looks like CX frames are heavier than road frames these days by a large percent. 1 lb doesn't mean much to many, it seems, but I call it, oh, about a 28% weight increase with no detailed explanation of why/where the weight is needed. Frame hype has many details but not this, apparently.
I note that in the 80's/90's that CX bikes were mostly roadbikes or CX specific bikes that weighed the same or LESS than road bikes. I don't recall any rationale for heavier. Also, I do strongly note that CX courses are often much smoother and easier nowadays. Lastly, back then a fat CX tire was 28 and absorbed LESS shock, yet these light frames did fine. Today's CX frames fit up to 35mm -- very cushy. Well, maybe roadframes these days are made so much more fragile that CX frames have to weigh more due to mystery reinforcement. Is it well known where the extra pound-worth of material must go or a frame will break in normal CX usage?
Material plays a big role. I'd wager that in the 80's/90's most CX bikes were steel. You're looking for aluminum and that has a radically different fatigue life. Al can handle very little flexing before the material fatigues and cracks. No matter how tame your CX courses are, the dynamic load stress on the frame from riding high speeds on bumpy surfaces is significantly higher than riding on the road (though when it comes to Michigan roads, the difference may not be as great as elsewhere ). The only way to prevent aluminum fatigue failures is to keep it from flexing. The way to do that is add material. Note that fat tires don't change the magnitude of the low frequency forces on the frame, they just filter some of the high frequency content.
Now, it's possible that a smaller rider on a well groomed course could get by with a lighter alloy frame and not push it into the fatigue range, but the big brands don't build for the 5th percentile. What you describe is a custom tailored frame, so you're going to have to go to a custom builder and pony up a bit more than a $200 ebay price tag. When it comes to alloy frames: strong, light, cheap ... pick any two.
"When dealing with stuff like this consider that this is a bicycle, not a spaceship." -- FBinNY