Bugginess of one particular implementation (and let's be fair here -- most of the stuff in glibc is quite ugly and hacky, a direct consequence of the bazaar model) has nothing to do with dynamic linking. Both PAM and NSS have been used successfully in a dozen of other operating systems for decades, and that's dynamic linking that facilitated these technologies.
Are you arguing that glibc code quality will magically go up if they abandon dynamic linking?