Headings should always be short, never a few sentences, so I do not think you wasted your time. Without seeing the document I can not offer an opinion of whether there was a better method than nested lists.
Thank you. I wanted to provide a short clip of my file in case you had time to look at it, but haven't yet had time to clean out all the confidential language. I'm glad for the confirmation that it was probably not a time waste. It was demoralizing committing an extra two hours to a project only to wonder if it was for nothing.
Good to remember -- a primary & fundamental "shall" for an accessible PDF (by definition that'd be a PDF/UA-1 compliant PDF) is that the appropriate PDF elements/tags be applied to the content. The lotsa-heading elements you've described would not pass this requirement.