I suspect the evolution of beer is quite a bit more complex than that. Beers have been brewed from a wide variety of grains, and the colour was mostly determined by what exactly they used. Subtle mixes are a fairly recent thing, and while the mass market beers are usually pale, darker beers are still very popular too.

> I don't think this means the tomato-based modern pizza is less of a pizza

Quite the contrary, it's more of a pizza.

I've seen pizza bianca in my supermarket. I do wonder, if you don't put tomato sauce on it, what's the fundamental difference between a pizza bianca and a flammkuchen?