Keeping old SEO with new site design

Site URL: https://www.autonettech.com

We redesigned our website, and because we changed the template we had to do a brand new site instead of just updating the old one.  We're going to transfer the URL from the old one to the new one.

My SEO person wants me to leave all the URLs for all the pages in the old site intact, because they are indexed in Google.  Some of those pages weren't included in the new site, because we didn;t want them.  My question is,  can I just create those pages but leave them unlinked in the new site structure to achieve this?

Am curious - if the domain name didn't change, is the new content on the new site not using the same URL? That may cause the SEO to take a temporary dip but, remember, eventually SEO is not based on links alone but, content. Meaning, if you changed your content - add/change/remove - that is what will impact SEO.

Direct answer to your question - my suggestion is to redirect those old URLs to relevant content on the new site instead of pointing them to unlinked pages. Navigation (menu layout) is a variable in SEO ranking so, having pages there that are not part of your menu but, still accessible via a URL because they are visible may lower ranking. Then, there is the issue of whether those pages have duplicate or similar content to the new ones you created. Now, the crawler is confused as to which one to show when matching a search query.

Bite the bullet and do it right.

@pinoshah