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.
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.
Red meat - carcinogens appear to come from preparation methods (browning, curing) and can be mitigated by vegetable intake. https://examine.com/nutrition/does-red-meat-cause-cancer/
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."
Mostly plants is one of multiple ways to an optimal diet.
That seems like an odd turn of phrase.