If the JAX-RS fraction is used (e.g. autodetected because of some dependency), default deployment is JAXRSArchive, because DefaultJAXRSWarDeploymentFactory has priority. This happens even if JAX-RS isn't actually used.
The problem is that if JAX-RS isn't used, there's no JAX-RS Application class, so JAXRSArchive auto-generates the default one, which maps JAX-RS to /. If the application uses servlets, these are now hidden and can't be accessed.