It's weird. Youtube was and is hardly the only platform of its nature around. But the way in which it's emerged as something of a digital landscape unto itself is staggering, and basically shapes how most of the internet is today.
Where do big production houses first launch trailers for their products? Unless it's a livestream, in which case maybe Twitch, then it's Youtube. Where does the 'Let's Play' industry centre itself? Again, other than Twitch which better suits livestreaming, Youtube. If a new startup wants to put out video content but cannot get itself into the good graces of a television network they will inevitably go to youtube. Even creators with their own websites and separate video players will still use youtube because it provides them the greatest amount of exposure and thus interest in their work. Youtube has developed in a way that few other platforms will ever be able to reach, and has become something of a first stop on the internet for the western world. It raises a hell of a lot of questions in doing so, given it's a company that thousands of people rely on without really working for, and there are few viable alternatives to it in case say, advertisers flee en masse because some of the bigger names turn out to be racists. But its sheer significance in the modern internet cannot be denied.