I wasn't saying that Nostr is small. I think it is a good size for any service provider to play the game. But the apps themselves are way too small for payment integrations. And they will always be small.
Apps on Nostr are like Watch faces. They don't have the time to build the supporting infrastructure to redirect cash.
On the second point, yes, people trust Amethyst more than a service they never heard about, but that is fixed when Amethyst recommends services in a settings page. We pass the trust we have to providers. If we just code a WoT settings screen where you are one of the providers, users will click on it and create an account with you. The better the integration, the better the capture.
That's also why I think we need to have WoT-visualization clients whose only job is to "sell" how web of trust is better than everything else. Then users just need to pick a provider and use in all apps.