As long as the guidelines are controlled by the USDA, the guidelines will favor the USDA. Let me illustrate with (probably) a hypothetical analogy. As long as transport regulations, Laws, safety standards, tax credits, research funding, etc, are controlled by petrol-powered car makers, regulations, Laws, safety standards, tax credits, research funding, etc, will favor petrol-powered car makers, as opposed to any other form of transportation like motorcycles, electric vehicles, mass transit, and so forth.
Another way to explain.
How it works now
Producers decide DGA - consumers consume producers' product
How it should work
Consumers decide DGA - producers produce accordingly
The point is producers must have no say on DGA. Instead they must be made to produce according to certain standards for nutrition and health for example. One idea is to impose a quota for certain foods prescribed by DGA, maybe a % of total production. In this example, wheat producers couldn't produce more than, say, 20% of their total production as wheat. Ya, they wouldn't be wheat producers anymore, but that's the point.
Also, since DGA dictates production, this production should then be funded with tax credits and grants accordingly.
It's pretty much unreasonable to expect everybody (the consumers, those who would decide the DGA) to know anything about nutrition and health, but it's also reasonable to expect anybody to desire health and fitness and leanness, rather than sickness and obesity. So, to bypass this problem, it's simple enough to determine what makes us sick and fat, and what makes us healthy and lean and fit, then design the DGA accordingly, and in turn impose quotas and such on producers.
Finally, the DGA cannot be monolithic as they are now, favoring a single group over all others, both from the producers side (wheat vs meat for example) and from the consumers side (low-fat diet vs low-carb diet for example). Instead, the DGA must include all possible diets (whether healthful or not, but if not, then ways to compensate like certain supplements like B12 and fat-solubles for a vegan diet for example) and provide equal support for each, so that consumers have a choice, but also have ample support to maintain that choice. In this way, diabetics type 2 for example would have a wider choice of diets, instead of the single diet prescribed by registered dieticians and nutritionists, which by the way says to eat at least 240g of carbs per day (I've seen it with my own eyes). Indeed, registered dieticians and nutritionists would have no choice but to be taught and learn about all those other diets that do not necessarily say to eat lots of carbs, like the Atkins diet or The Zone or whatever you can think of. Their curriculum would have to be revised to reflect the revised DGA, the supporting experiments that determine adequate nutrition and health, and so forth. RD's could no longer act as simple sales reps for producers - even though they don't see themselves as such, that's how it is now.
OK, so I won't give them this comment or any comment in fact, you guys take what you want from this and do it yourselves.