For example, you claim that Vimeo "vimeo has all of those [features] to some degree".

But it doesn't. Vimeo isn't ad supported (this is literally their main differentiator from youtube). Doesn't appear to do algorithmic curation/recommendation (again, they consider this a differentiator), and has a tiny fraction of the upload rate and watchtime of youtube (so bandwidth and transcoding cost are lower).

Those are related to their distinct strategies: Youtube aims to be the product where anyone can share video for free (that's youtube's strategy!). Vimeo doesn't aim to do that. Doing the first invites challenges of scale that the second doesn't. Youtube operates at a scale where it makes sense to hire silicon engineers to build custom video transcoding chips. That doesn't make sense for vimeo.

You can maybe argue that Youtube was only successful because of Google's existing ad business (although I don't know how true/organizationally valid this argument is), but the idea that the "strategy" behind Youtube was to be illegal is sort of ridiculous.

And heck, OP of the thread even offers examples of successful competitors in the broad video media space: Twitch and TikTok (and arguably also Instagram via Reels). Youtube does have competitors in terms of video social media. It also has competitors in terms of video hosting. What it doesn't have is competitors in terms of scale (Reels and Tiktok limit content size, Twitch stores only a small fraction of streamed videos, vimeo makes you pay for the storage and bandwidth you use). That's due to a lot of technical optimizations that are difficult to replicate.