I often upload empty layers into AGOL for use in JS web applications for data collection. Everytime I upload the layer I am required to configure the layer in the AGOL Web Map Viewer and save a Web Map. There should be an easy way to configure a layer in a web map and simply change the feature service it is pointing to.
This is very similar to the ability to change the data source of a layer in ArcGIS Desktop.
Similarly, it would be very helpful to be able to do the same thing with a web map configuration.