I can't think of anything a sitemap is used for that requires content split up by content type. Can you dig into that a bit and give us a more detailed picture of what is being created, how it is being used, and why it would want to be edited?
The big worry is the pages that aren't being generated--that is content that Google and other search engines aren't seeing (or are seeing only to the extent that they follow links from pages in the site map). That would be where I would spend time before anything else.
Related to this is the possibility that you are also using a variant of your site map to help people find things on your site. That is usually not useful with a site as large as yours, which would raise the question of how people navigate, what are they looking for, how do you convey a "scent of information," etc.
We often think of websites as places where people land on the home page and then wander about. In reality, they land on the page that a search engine or link suggested would answer a question or meet a need, and then do some minor exploring (or, most often, go on to another website). So, I also raise the possibility that there is an architecture and/or SEO issue--but that takes us far afield from the question as it was asked, and gets into analytics telling you how people are using the site, and then using that as a guide for further development.
In short--a site map is a shortcut invented to help search engines find your content. Need to understand better why you aren't getting a whole site listed, and what you are hoping to accomplish by editing.