I'd say it's evidence that the class is self creating, but not specifically that the class is necessary for society to function. It could be for instance that it must necessarily exist, but only as a byproduct of society (e.g. some people have slightly more resources and therefore an advantage to press to get more resources etc.)

Or possibly it's just a consequence of the kinds of society we've had up till now. Perhaps in [your favorite utopia] it's not necessary nor beneficial.