Where's the irony? Unlike social media platforms, which can ban you and make you lose all your followers (it just happened to me on X), with Substack you can export your audience and continue elsewhere if you can, without losing a single contact.
It's still a closed garden not under your control.
That's partly true—if I leave, I lose the infrastructure for creating articles and sending newsletters, but I can take my contact list with me and use another service. It's like email. If I change my email address, I can export my contacts and use another service. A true closed ecosystem keeps everything—the infrastructure and your contacts—all in one place. Look at social media.