Unfortunately, this is correct - in order to make use of one of our templates, you would need to use the steps you describe, making the change to a saved listing or recreating a listing and applying the template, then using the HTML on the Revise Your Item form on eBay.
Please keep in mind that the scrolling gallery can be added to listings, but using a template affects the formatting of the entire listing, and so they are not able to be added in the same was that the gallery can.
Please also note that you can set your account preferences to not use the scrolling gallery so it is not appended to your listings, and the Manage option from the Gallery menu of your account will allow you to make changes to your scrolling gallery preferences. Please note that changes made to your gallery preferences only affect the gallery on listings posted after the change. If you make a change and would like it to affect the active listings, please file a support case and let us know and we can run commands to remove it and then re-append it with the new preferences.
I have forwarded your comments regarding the templates and a tool to add them to already active listings on to our product management team for their consideration and will update this thread should more information regarding this become available.