Well nutrition isn't exactly a settled science. There are many problems with studies and as a result we have a wide variety of sometimes contradictory conclusions from them. New conclusions and findings come out but the nutrition community is unable to achieve a consensus understanding on these types of aspects of a diet. There are too many confounding factors involved in studies and it is nearly impossible to design a study that will show the exact effects of eating bacon on the diet without other dietary considerations tainting the results. Like for instance lots of new studies are coming out recently claiming that our disdain for saturated fats is highly misguided. However, nutritionists cannot come to a consensus because old school people stick to what they learn in school without keeping up with studies, people distrust the new studies or argue in favor of the many contradictory studies, etc...
The science is settled, but like everything else, untrained people can't tell the difference between a good study and a bad study, and the media reports on them all.
Check out the book _How Not to Diet_, which is the most recent masterwork on evidence-based nutrition.
It doesn't take a ___domain expert to know this claim is fundamentally wrong. Science is never settled. There are conclusions that stand the test of time and accumulated evidence, but nutrition is a field with precious few of those.
I would not agree with those government diets, without some nuance sprinkled in. Calling all the government bodies published guidelines "scientific consensus" isnt the same thing as scientific consensus.
Vegetables - way too broad a category. Should be split into leaves, stalks, roots, starches, seeds, alliums, brassicaceae, legumes etc. Calling it all "vegetables" makes it hard for people to rank, prioritize, and proportion which are a better use of time, money, and energy to consume. There might be consensus on eating "vegetables" but not necessarily every group of them.
Nutritional density is more complicated than "vegetables."
Whole grains - Antithesis to previous point, grains are not categorized as vegetables. Why are whole grains their own recommended category everywhere as a staple part of diets? Is it cost? Industry lobbying? Diet recommendation should focus on leaves and seeds, with cereals as a filler. Cereal portion should be the one controlled to control weight gain, moreso than plant fat from seeds/nuts. We've gotten too comfortable with a huge serving of rice or potatoes with something thrown on top.
Fruit - mostly as not necessary to a healthy diet as this makes it look like. Can be avoided the same way meat is.
Fish (salmon & sardines) and Seafood (mussels) belongs in the consensus part over fruit.
Doesn't touch on fermented food.
The jury is more out on saturated fat and dietary cholesterol than these government bodies want to admit.
Its hard to reverse course quickly and say "everything we said for the last 30 years is wrong."
Almost none of the diet suggestions focus on digestion, absorption.
I just dont see consensus on what percent of a diet should be grain vs vegetable, starches, legumes, fats, meats. Maybe it doesnt matter. "WFPB is the healthiest diet" is very different from "WFPB is one of the healthiest diets."
