The OP never said that "being the product" had anything to do with privacy. It doesn't have to be about personal data, that was your own strawman. What social media platforms "sell" is, mainly, interactions.

Also, and I repeat this, you don't know what personal data you share when using a proprietary app. If you use Nostr, you know exactly what you are sharing.
You have no clue what data a proprietary app will share. It may have all sorts of identifiers. You don't have the source code. You don't know.

So even when it comes to personal data, Nostr is widely different.