YouTube is the one-stop-shop of internet videos. Any specific niche has a competitor, but none of them seriously competes with the whole of YouTube.
I noticed the outage because I wanted to watch a stream, so I might go to Twitch now. Often I use Youtube for music, where Spotify is a solid alternative with many of the same creators. If I want to see that video from reddit of people throwing burning flares at a balcony I can probably find it on LiveLeak. Many of the educational channels I've subscribed are also on Nebula, but I could also watch a documentary on Netflix or Disney+ instead.
My daughter could not do her homework assignment, her Google classroom is linked to YouTube. Thank goodness I was able to find the video she was looking for on Dailymotion. I haven’t been to the site in over 10 years
LBRY and Bitchute can automatically mirror your YT channel, and IIUC the former can also automatically upload videos to YouTube, maybe even on a customizable delay. Some decent sized channels like minutephysics use LBRY, but even though anecdotal accounts report much higher revenue per view and no decrease in YouTube exposure, it’s still certainly a uphill battle to compete with a de facto monopoly that can afford to hemorrhage money and just get more from a massive gatekeeper of the web.