I think this is a bug, but I'll start out as a question.
I want to make a web map using tiles stored in mapbox.
Notice how you can zoom into zoom level 21 in the mapbox viewer.
When I add the mapbox tiles to a web map (Add Layer from web> Tile Layer) I'm limited to zoom level 19.
http://ambergis.maps.arcgis.com/home/webmap/viewer.html?webmap=18ebe9346a4a4eecaf1ef76b83e8d31e
Using the javascript api, I'm able to workaround by creating the layer first, adding lods to it, then using the lods to create the map and a new layer.
http://ambergis.com/domain.html
I'd really like to be able to use an arcgis online webmap to mapbox drone imagery at zoom levels greater than 19 in a webmap.
Is this a bug?