Fiber being a type of carb is also found in other high carb foods like beans, whole grains, potatoes (with skin), and popcorn. Beans are the best source of fiber by a mile in terms of quantity.
I don't think I said anything of the sort. Regardless, fiber is food for the microbes in the gut. Eating fiber from a diversity of sources is important as well as quantity.
Black beans, kidney beans, white beans, garbanzo beans, lima beans, black eyed beans.... we can go on if you like. Don't forget the huge variety of lentils as well.