my specific examples was about herbs but it's valid for almost every food category:

* meat: my family is from a village near Rome, Roman traditional cuisine is famously full of recipes that use all sorts of weird meat cuts (pork jowl, internal organs of various animals...) - you won't find most of those in an average supermarket. When it comes to meat, the problem is not just cuts, but also breeds: I live in Australia and it has been extremely hard to find chicken which is not Cornish Cross. In Sydney, you can find heirloom breeds chicken at only a handful of speciality butchers, and prices are very high.

* grains: this is a well known problem, most grain-based products are based on just a handful of varietals. I have to say that the situation is starting to improve: recently, in some upmarket stores, it has become possible again to get products based on some heirloom grains, however they are pricey (example: Pasta Monongrano made from Matt or Kamut flour)

* fish: it is a known problem that fishing boats are forced to throw away certain catch, because certain fish varieties are not "marketable"

the list could continue...

Fair enough. I'm not sure if those foods were any better or worse, but there's definitely an argument to make for the poverty of variety of modern cuisine.

yes, exactly, the problem is not whether those are more or less nutritious, the issue is the lack of variety. It seems that gut bacteria only improves if your diet is very diverse. But modern industrially produced food is made from just a small list of commodity ingredients. If you are curious about these topics, you could check out "The omnivore's dilemma", a book by Micheal Pollan, or the video documentary "Food Inc." that is also narrated by Pollan

I'm not sure if the gut microbiota "improves" in adults at all. It's largely established by the time you're past 3 years old, and even radical dietary changes mainly just shift the relative abundances around.

There's probably still an effect in there, but it seems more likely that it's mainly antibiotics that are killing off gut microbiota variety, with an argument to be made for a role of highly processed foods.