I notice that it will be created as
<div> under <div> with class="esriMapLayers"
<g> under <svg>
where all the feature layers are loaded into
I think this maybe the reason why reorderLayer does not work for ArcGISImageServiceLayer.
I'm ok with any method as long as I can do reordering of ArcGISImageServiceLayer with FeatureLayer.
Alternatively, is there any way I can display a raster image that support reordering?