The one thing that might be helpful to add here is that the [serviceURL] was changed to https://demos.telerik.com/reporting/api/reports and the [reportSource] to 'report: 'Telerik.Reporting.Examples.CSharp.ReportCatalog, CSharp.ReportLibrary''. Also <link href="assets/all.css" rel="stylesheet"/> needed to be added into the header of the index.html once the css and html files had been copied to the assets folder.
There may have been one or two other details but I think that was the bulk of it.
The main reason I'd like to write those details out here is that I'd rather anyone else who has the same issue be able to refer back to this thread and find what they need. As for whether the Report Viewer installation directions could use any updating or further consolidating of information I'll leave that to the discretion of the Telerik team.