I'm a bit new to this, but I ended up sorting this out using the createFeatureLayer() method on the sublayer for anybody having a similar issue. I also changed the way I organized things quite a bit but for what it's worth, I included my code below. The selector widget sets a definition query on the map based on the values (that were manually loaded, along with an option for "Default Extent") and then pans to the centroid of the selected zip code. This is for a 2d map feature in a SceneView with a different spatial reference than the default. If there are ways to clean this up would be happy to know.