IMO, maxing out at either end of carbs vs fat is not such a good idea. Sure, you can go with almost no fat, but you'll be carrying more weight to do it, and if you're like most people, you won't find your foods as satisfying as those in a more balanced diet. And while you could probably live on a diet of 90% olive oil for a while and save some weight, you'd get sick of it pretty fast. (In my experience, most people get disgusted by a super high fat diet before they reach the point that evidence shows they'd be having a problem from too few carbohydrates.)
Reasonably healthy diets from around the world include a wide range of fat/carbohydrate ratios, and so can backpacking diets.
When I took my first shot at what a week's worth of food at would look like, it was just over 110 cal/oz, nearly 50% carbs and a little less than 40% fat. I'm used to eating a lot of nuts, and my first shot included Nido, so my first shot was higher fat than some people's might be. (This is a 3000 calorie/day diet on which I'll lose about 1/2 pound/day if I'm doing full trail days.)
When I finished tweaking it, it was more like 125 cal/oz, < 40% carbs, ~ 45% fat, and I'd saved about 1.2 pounds. Was it worth it? I'd say so, but it was a challenge! Things like the refried beans and instant potatoes I mentioned have essentially *no* fat. It takes a lot of Nido at 50% fat to make up for that. Parmesan/Romano was a tasty way to balance the potatoes. Hummus at 40% fat will never get me there, but it's pretty balanced on its own, and it's good.
So at least when I say I'm pushing the fat to keep the weight down, that's what I'm talking about – the challenges of getting it up to 45% or possibly 50% – well short of a diet of butter sticks dipped in peanut butter and olive oil, and well within ranges that should include adequate carbohydrates.