Both is true: YT has expanded democratic publics by lowering barriers for content creation and distribution; and it also has subverted democratic publics by amplifying extremist, emotionalising or propagandistic content.
To give another example, it is YT's monopolistic market dominance that makes it so strong and valuable as a market place for creators and users alike; at the same time, the proprietary governance leads to discriminatory practices such as shadow bans without accountability. 2/3