Are you going to argue qBittorrent isn't a product because it's a "presentation of open protocols"? Of course it's a product too. Mastodon is an app on the Apple and Play stores, with a back end that's federated. You don't get much more "product" than that.
It's entirely possible to focus on a good onboarding experience for new users and a good long-term experience. It's not either/or, that's a false dichotomy.
And the idea that we don't have experience of social networks "designed for long-time users" is ludicrous. Virtually every social network out there wants its users to stay for a long time. And with Facebook and Twitter, there are many users out there using them for over a decade.
The idea that we "focus too much on new users" is just bizarre, when the reality is that Mastodon isn't focusing enough on that.