Although plants make up only a small fraction of my caloric intake, because they are much less dense in calories, they make up a large fraction of the mass (and volume) of the food I eat.

Those veggies are mostly fiber. Fiber is technically carbohydrate (hence my putting "carbs" in quotes earlier), but unlike most of the carbs in the typical person's diet, the fiber in the plants I eat doesn't get converted by my gut or my body into fructose or glucose, so fiber is OK for me to eat.

Most of the plant foods people eat that aren't loaded with the kind of carbs that get converted into fructose or glucose are loaded with oxalate, which I have tentatively concluded is a problem for me. Cabbage, cauliflower and radishes are extremely low in oxalate, for plants. Fennel is not particularly high, but also not particularly low in oxalate, so on days I eat fennel I take measures to encourage prompt elimination of the oxalate (i.e., I eat fennel only during the first meal of the day and I make sure to get plenty of calcium every meal that day).

Anyway, did any of these people try reintroducing plants in their diet? If not, at most we can say that a change in diet caused these improvements. We cannot say that plants are somehow a contributor to disease.

In fact, I've heard the same anecdotes as yours, except the diet change was the exact opposit: People who stopped eating meat and saw incredible changes to their health. These anecdotes and yours have one thing in common: Change.

We have good evidence that the gut microbiome can change its composition very quickly, in the manner of days, based on food intake. It's possible that some part of the microbiota were reduced or boosted as a result of the radical shift in the diet, and that you'd see a similar effect if you went meat -> plants.

If you're a science-minded person, you could try introducing specific things you eliminated, one by one. That is the principle behind an elimination diet, after all. For example, add broccoli for a week and see what happens. If you get worse, maybe it is the plants.

To be clear, it's quite possible for a temporary elimination diet to aleviate unexplained symptoms, for instance from an unknown food allergy or intolerance. But then you need to slowly reintroduce foods to find which specific food causes the problem, otherwise your diet is bound to be nutritionally deficient. Eliminating all plants from your diet permanently is insane.

An anecdote isn't that persuasive, talk is cheap. Systematic reviews of randomized control trials won't show a carnivore advantage over whole foods. There's no compelling evidence, this is just brushed aside with conspiracies.

Notwithstanding that in the first place there's evidence that whole foods (plant-based or not) diets can improve life extension and profile.