Google has monopolies in advertising, mobile, streaming video, mapping, and web browsing. The latter gatekeeps all other Internet based businesses and allows them to pick winners and losers.
YouTube is a monopoly. Arguably it's one of the largest social networks too. But for most video creators, YouTube is the only option to reach an audience. Bear in mind, even big movie and TV studios who operate their own video streaming platforms... where do the trailers all get posted? YouTube, where people can find them.
As someone who's not used Google services since 2016... it's still the one Google property I can't really escape, because nobody is posting their content anywhere else.
Maybe in the most narrow of definitions. IG/FB and Tiktok are huge competitors in the video space, Tiktok being the dominant platform if you focus on short form video.