FYI: The Imagery Development team have release a collection of widgets that are specifically designed to work with image services. They're available for download from GitHub.
Image Service Widgets for Web AppBuilder for ArcGIS | ArcGIS Blog
Sample demo app: http://esriurl.com/LandsatOnAWS
Download link: GitHub - Esri/WAB-Image-Services-Widgets: WAB widgets specific to image services – WABIS