People have also successfully gotten videos taken down from youtube by claiming copyright to bird noises that doesn't mean anyone owns bird sounds.

It's understandable for Microsoft to follow the DMCA notice and take down procedure but none of this adds legal weight to a "creative" reading of the law. If something isn't clearly in line with the clear text of the law it means exactly jack shit without a actual court decision backing up the lawyers interesting interpretation of the text.

Its insidious because it probably wont be settled at all and the settled truth is that you can mostly abuse the DMCA to have anything taken down for 2 weeks unless they have the funds to sue you for it.

Future imitators will presumably be toolkits where you plug in your own "channels" and will be promoted as tools for people create their own youtube competitors.

With a bit of work you could probably have actual non infringing users for example a provider of tech or how to videos with a more generous sharing arrangement compared to youtube.

You can own a bird sound just as easily as you can own a picture of a bird. In the copyright sense of "own".

The law defines whether a document qualifies as a DMCA takedown notice, not the manner in which the document is being used. Somebody other than a court declaring a document to be a DMCA takedown notice doesn't make that true.