I've never worked with a web application where the requirements of the "customer facing API" and the "drives the web application API" (or the "drives the mobile application API", "drives the internal admin app API", etc.) matched for very long, if ever. Customers will usually need a small subset of the API that your web app does, the authentication will likely be different, you will need to make optimizations in your web app fetching that will be highly tuned to your specific use case, and a whole bunch of other concerns that make the idea of your web application being driven off your public API unrealistic.