Substack has 250,000 paying subscribers and its top 10 writers bring in $7m total per year, according to Forbes (https://www.forbes.com/sites/falonfatemi/2021/01/20/the-rise...). We might guess that each subscriber pays $10/month, which would add up to $30m annual revenue.

The New York Times alone has 7m paying subscribers (https://www.nytimes.com/2020/11/05/business/media/new-york-t...). The cheapest subscription is 50c per week, so that's at least $182m revenue per year (in fact that's an introductory offer and the standard rate is four times that).

But Substack is growing! Yes, but so is NYT. In fact it signed up half a million new subscribers, double Substack's total, in the first quarter of 2020 alone (https://www.niemanlab.org/2020/05/the-new-york-times-success...).

Maybe the NYT is too ambitious a target. OK: the LA Times, which is "in crisis", has 356,000 digital subscribers (https://www.thewrap.com/los-angeles-times-crisis-stalled-sub...).

So, I'd say your argument is not proven yet. Wanna take a bet on when Substack total subscriptions will overtake the NYT?