You're confused. Google does not know what sites are receiving DMCA notices. They have no omniscience of communication between content creators and websites the

You're confused. Google does not know what sites are receiving DMCA notices. They have no omniscience of communication between content creators and websites they don't own. They will not be taking into account notices sent directly to YouTube or any other site in ranking search results. The new ranking signal is the number of DMCA notices sent to Google for each site, not the number of DMCA notices the site is sent. Google receives DMCA notices to remove search results pointing to infringing content. Google receives these notices primarily for sites that are outside the US and would ignore DMCA notices sent to them directly. They would not receive any significant number for YouTube videos because YouTube handles infringement directly; there's no reason to send a second notice to Google to pull the search listing. (I'm aware Google owns YouTube. That does not change anything.)