A fan wiki earns trust by being specific. A page that says a creature is strong is filler; a page that lists its exact counters, numbers and patch history is a reference.
Structure matters as much as accuracy. Creature pages should share one template: stats, evolution path, element, counters, and the patch where behaviour changed.
The final ingredient is maintenance. Pages that note when data was last verified age far better than pages that silently drift out of date.