Orphan pages of a News/Publishing/Magazine Site. What to do?

Our client is a News/Publishing/Magazine business with 8 sites. One thing that we've noticed is that they have a lot of orphan pages. They have thousands of pages from 2005-2018 which we see as old pages that might not be helpful now. My teams initial plan is to deindex/remove from sitemap/delete the old pages (which I tend to disagree, because I said that if it is a publishing site, even the page/news is old it is still important to the website because they are publishing company) and with the newer pages (thousands of orphan also) we plan to internal link it. Is my suggestion not to deindex/remove from sitemap/delete the old pages is right? Also, I 'm new with news site. Is it normal that they have many orphan pages? One reason I see is that they just added news at **"Related Articles," "Latest News," "Trending,"** or **"Recent News"** area. Thank you in advance!