How to transfer the site from the point of view of search engines?

Question

Google

Hello everyone, the essence of the matter:
- there is a functioning IM with about 5000 pages in the search. It has a wrong URL logic:
-- Site->Category
-- Site->Product
-- Site->Other page.
Now there is a transfer of all this goodness to a new engine. And the question is whether to leave such a structure so that the pages do not disappear from the issuance or remake them through a 301 redirect for a normal view:
-- Site->Category
-- Site->Category->Product
-- Site->Another page.

Answer 1

Our experience is not to change the structure of URLs!
First, reindexing is long and painful.
Secondly, anyway, in the new engine, you always need to remember about the old structure, because. there are probably natural links to old pages left, so the redirect should work correctly for the next 5 years.
Thirdly, users do not care, they do not delve into either long or short URLs, Safari does not show the path through the site at all, only the domain in the address bar.