Substack knowingly and openly platforms neo-nazis, allowing them to profit from their rhetoric while taking a piece of the action. Even if the authors avoid specific calls to violence to skirt the ToS, it still gives them fertile ground for recruitment and funding of their activities.
By your definition, then, Substack should be labelled as a terrorist organization and shutdown, yes?
Writing about your Neo-Nazi beliefs, or even being a Neo-Nazi doesn't make you a terrorist, and I'm sure none of those you're talking about are. So no, by his definition, Substack shouldn't be labelled as a terrorist organization and shutdown.
Worse, Substack promotes nazi content via push notifications to people that haven't subscribed to those nazi accounts.