“The entire “controversy” was based on what people thought the Fine Brothers would do, not what they did, and that’s pretty terrifying.”

Not exactly. The controversy was over what the Fine Brothers could do. The idea of trademarking “React” allows some (although agreed not very powerful) legal recourse. YouTube has been known to, when a legal stick no matter how big it really is gets waved under its nose, to just pull content and ask questions later if ever.