This is far too dismissive - I'm guessing you don't run a WordPress agency. We don't use WP Engine for hosting, we only use the ACF plugin. ACF is not "very easily replaced" because we've built the site data structures around it and we'd have to completely rearchitect the sites - at our own cost. "Moving our sites" is not easy either because we have 100+ sites, each of which would involve DNS updates (which we often have to walk our clients through because they don't understand DNS at all) and a complete reconfiguration of our build / deploment process. I don't really understand the motivation behind this comment.