The script is just a reference for you.
If you need to keep the author of the items, you need find the mapping relation between the survey lists in your site and sub site.
If you want a simple way, try a 3rd tool like APElement's FLY.
https://www.apelements.com/products/migration
Justin Liu Office Servers and Services MVP, MCSE
Senior Software Engineer
Please Vote and Mark as Answer if it helps you.