Best for SEO - Transfer or Connect Domain for new SQSP site?

When creating a brand new site & domain for a client using SQSP for both, the SEO optimization process was a breeze.  For another client, they wanted to keep their domain hosted with GoDaddy but create a new site with SQSP.  After launching the site, SERP ranking/results tanked and SEO optimization was a lot harder.

I know there is A LOT more than just domain transfers that go into SEO, but any recommendation on whether to transfer or connect domain? Does it seem to work better when everything is consolidated with SQSP and their platform?

Thanks for any advice!

There is no need to transfer the domain to SS. It sounds like the projects were different - one was a brand new site and one was a migration. Designers should encourage migration clients (or any client) to consult with an experienced SEO.