I think while some niches are indeed extremely crowded, claiming that YouTube as a whole is saturated is a bit of an exaggeration. If you enter a major niche and simply replicate what hundreds of other channels are already doing, success will naturally be difficult. There is still room for growth, but average content faces a much tougher landscape than it did a few years ago. Channels need to innovate and improve the quality of their content and perspectives; simply repeating the same old formulas is unlikely to yield good results