I strongly disagree. If React's API were to get all big and complicated, that would be a concern. The tight scope and clean interface are definitely selling points for React compared to many larger (in scope and interface) frameworks and rendering libraries. But I really don't care about the file size, as it's far too small to be anything but noise in almost any web app where it's worth using a tool like React at all, and it's going to matter less anyway as JS build tools get more sophisticated and connection speeds increase over time.