> AFAIK ContentID claims mechanism merely mimics DMCA mechanism
It doesn't even do that, nor is it intended to. This isn't bypassing DMCA, though.
> That means you can throw automated infringement notices at users knowing that X% of them will be false positives. That wouldn't work with DMCA.
Sure, but DMCA isn't even relevant. DMCA notice provisions are a requirement for content owners to bypass the DMCA liability shield for third-party hosts in filing infringement claims -- they have to file notice in accordance with the DMCA, and then if the content host doesn't act within the parameters of the safe harbor, they can pursue whatever infringement action they would, absent the DMCA liability shield, have had against the content host.
DMCA notice requirements do not protect users from infringement claims, they protect content hosts. (And counter-notice requirements protect content hosts from liability claims from users stemming from take downs based on the DMCA notices.)
There are no DMCA provisions that exist to protect users posting allegedly infringing content.