Bantams, generally, are ornamentals. However, we can enjoy all that we do in large fowl, in bantams. Many cannot keep, breed, and raise quantities in large fowl. Therefore, they enjoy the hobby in bantams. They also are more likely to be able to enjoy more than one breed.
I say this to say, that there is nothing wrong with bantams.
Concerning utility, some bantam strains have potential. Particularly along the lines of feed efficient layers. Bantams mature faster etc.A bantam x large fowl can produce 1/2 size birds that lay 3/4 the size of eggs. That is half the feed for 3/4 the egg. This is the concept behind some strains of commercial leghorns. These concepts have been realized for some time. There are down sides to, of course.
But, this is not keeping with the preservation ideals of this thread, which I agree that there is a need. I like the originals first, and my first love. I like to see all of our breeds well represented in the original large fowl.