Not my field of expertise, but I think it's also possible to over-estimate the protection this provides. By the time sites are incorporating Google's own JavaS

Not my field of expertise, but I think it's also possible to over-estimate the protection this provides. By the time sites are incorporating Google's own JavaScript code, tracking cookies can be stored as the site itself. Only a single action (look how much data is handed to the site via the URL of a search result, for example) and this site-specific cookie is just part of wider tracking.