If you have thousands of pages and articles on the site, it's pretty clear that rewriting them is such a time consuming job!!!
Not the thing to do!!!
The best is to either leave them the way they are and simply direct less traffic to these pages and articles.
If a page is no longer accurate, it can of course be removed, especially if you feel that the content is outdated.
If the topic is visited a lot and there is a need for it, recreate a content which is appropriate for it in the form of a video. audio or e-book.
In some cases, the presence of that specific page or content in your site is symbolical. It means that it does play a role on an "energy level".
In that case of course it can be left there.
The best way to work through this "old pages" issue is really to use the navigation structure towards what is fresh on the site.
This is the top strategy to apply!