Yes. By number of users, Gab is by far the biggest fediverse/mastodon instance. However, because people [including it seems the article author] don't agree with

Yes. By number of users, Gab is by far the biggest fediverse/mastodon instance. However, because people [including it seems the article author] don't agree with the views of many of their users, they pretend it doesn't exist. It's not even listed on various sites which purport to rank such things. The irony of which seems to be lost on the creators of most of these 'alternatives', which trumpet openness and freedom from censorship. But only so long as the views you express coincide with their own.