Certainly, but unless the Google searcher can access the content behind the paywall without registration the website is not following the First Click Free rules

Certainly, but unless the Google searcher can access the content behind the paywall without registration the website is not following the First Click Free rules. If they cloak to Googlebot and don't follow FCF they'll be delisted, because as you said inaccessible content is by definition low-quality (in this case).