Legends have been a problem since the days of ArcIMS. I imagine that there are plans for building a much more configurable dynamic Legend Widget someday for ExB, but the way things work right now the legend widget just doesn't work well enough in some cases. Sometimes a static image would work better. It would be nice to have the option to simple upload an image or set a URL to reference one.
The Image Widget comes close to working for this, but when it is in a widget controller, you cannot change the svg icon for the button that appears in the controller. Another issue with the image widget is that there are fit and fill 'Position' options, but a 'none' option (the image is not resized) would be much better because the images become blurry from the resampling when resizing takes place with fit and fill.