Removing thousands of pages from the site. Won't hurt?

Question

Google

Hey!
I want to remove old pages from the site and from the search engine index. The site has approximately 10,000 pages, all in the index. Of these, about 5,000 are very old (over 10 years old), in my opinion, of poor quality (new pages are much better). Many of them are also duplicates (pagination). In Yandex.Webmaster, there is a constant mover - reindexing, then add, then delete some pages. So I decided to clean up the site and remove them.
Wouldn't such a significant reduction in the number of pages be a minus? Also, there are some links to them ...
If you delete it, then simply through robots. txt to prohibit entire sections and delete the pages themselves (templates), which would give 404. So?
Thank you. ;)

Answer 1

Well, what 404, why refuse traffic? 302 to the new version
as for which ones to delete - see Google webmasters

Answer 2

If you are sure that the old pages are of poor quality, and the new ones are definitely much better, then by removing low-quality content, you seem to improve the quality of the site as a whole.
In the end, who is stopping you from deleting these pages for a while, if it gets bad - return them?
It's a lottery anyway.