The Fairy type, while theoretically strong, has never been the reason any Pokemon has ever been strong. It is merely has only ever been the spice on top of a strong Pokemon, or even sometimes a hindrance.
No one has ever said they needed to add a Fairy-type to a competitive team for the sake of the coverage. Most Fairy-types are bogged down by mediocre stats. Moonblast could have its secondary effect reduced to 10%, but otherwise it's a decent type.
In practice, Steel is the most cancerous types. Too many resistances against the weakest types. Why hasn't Poison gained a Freeze-Dry variant? Merely removed the resistances to Ghost and Dark still isn't enough, as it remains the most dominant type in the game.