Google Maps use Mercator projection for browser-based maps. When Fusion creates a map that uses maps.google.com imagery as the source, it uses Google Maps projection for the rasterized vectors so that they match the underlying Google Map tiles. This EPSG code is EPSG:900913 or EPSG:3785.
However, GEE builds 3D data using the WGS84 datum (EPSG:4326). If you want to re-use 3D database resources, you can create a flat map using the Fusion Flat (Plate Carrée) projection.
If you build a Mercator-based database, you must build resources specifically for use with Mercator-based projection.