Your client is pissed, it is not easy to edit the content like he was expecting it would be. You don’t understand what the heck is the problem, you integrated everything, but so many options seem to be the problem even for you to edit, so you are in the position that if you want to make your client happy, you need to use your CMS and add content.
But, you don’t want to be a content editor, and you don’t want to lose your client. How to make a better approach, easy to use and make win-win on both sides.