In no way Schwarzbier might be as ancient. Black roasted malt was invented in the 19th century. Pastorianus yeast strains weren't used prior to the 16th century. They definitely brewed dark beers in Franconia back in the 800s and 1300s but these certainly stood far from the style we are talking about here.
When we are discussing (or setting competition guidelines for) Schwarzbier in the 21st century we are actually limited to a pretty narrow definition that comes from a pretty local tradition: a dark lager is called a Schwarzbier when it's brewed in a way traditional to Franconia between the 19th and the 20th centuries, where the style emerged and got its name. Although the style allows for some variations (though not much), straying further from the settled Franconian tradition leads us into the realm of Dark Lagers. What's wrong with our Crystal Black Lager to be called a Crystal Black Lager, not a Schwarzbier, which it isn't? Less exotic-sounding name? Well, there's plenty even more exotic names to choose. But the Schwarzbier "trademark" is "copyrighted" already, even if not by the law.
Rather (just like with most cultural phenomena) that was decades or centuries of practical brewing and local preferences which in time crystallized into a certain well-defined long-standing local tradition. People invented a style of beer. People invented a name for it. Am I entitled to appropriate what they've invented to serve My Own Precious And Brilliant Beery Сreativity? I don't think so. When I want a Schwarzbier, I seek for historical recipes and recreate them. When I want a Black Lager, I compile the recipe myself having no limitations other than my own preferences, and in such a case, "a Schwarzbier-inspired dark lager" or "a Schwarzbier-style Lager" labels seem legit to me.
I think, the world is already globalized too much to discard those already feeble elements of traditional heritage in favour of my personal "creative expression". So I don't dare to.
...Well, culture, tradition, heritage and history have been my professional field for all my life. That's why I have a bit of special attitude to those subjects. Which is extremely helpful in the hobby, I should add.