I think the biggest differentiation is that Pynecone apps are completely customizable and don't re render based on State changes. Streamlit is great for dashboard type apps but when you want to expand on your app you can be limited in terms of flexibility and customizability. The whole Pynecone website is made in Pynecone vs other frameworks like streamlit cannot do this because they are limited in what they can build.

See here for bringing your own components: https://pynecone.io/docs/advanced-guide/wrapping-react