It would be great is service definition files were hidden when searching for content in ArcGIS Online unless you specifically ask to see them. They clutter everything up and make working out what you've got difficult especially as they aren't deleted when you delete their associated service (Warn AGOL Users of Service Definition Files When D... - Esri Community)
As part of this is would also be great if the service definition was named the same as it's associated feature service and if this is updated when a feature service is renamed. And the description, terms of use etc. is also updated when these are changed for the feature service. That way when you do want to find the feature service it's obvious which service definition goes with which feature service. I know the service definition overview tells you the name of the associated service on the side there, but you have to open it to see that.
