Gab is not a Mastodon instance because its code base has been altered to the point that it no longer federates with any Mastodon instance or fediverse service,

Gab is not a Mastodon instance because its code base has been altered to the point that it no longer federates with any Mastodon instance or fediverse service, so that line of criticism is outdated at best. While Tusky has a great user interface, it is just one of many Mastodon clients and it is not developed by the Mastodon team. Also, Gab has a lot of content that is prohibited on Twitter, but allowed on a self-hosted instance of Mastodon. Mastodon would actually be of "greater openness" than Twitter in the case of Gab's content.