Like many things, it depends. I keep very few files in Google formats so I’m not an expert on backing up those documents. Yes, *.gsheet files on your local hard drive are just links.
Google has software that allows you to select which normal files that you wish to sync. If you choose to keep data in Google formats you can download them via Google takeout. This is a service that allows you to export your data either on demand or a schedule (ever two months for six months). Google’s “Office” documents will be exported as Word/Excel/Powerpoint files.
And if you have an important document in Google Docs, for example a Google spreadsheet, that you want to backup immediately you can right click on that Google document, select Download, and a copy in Excel format will be downloaded to your computer.
But most of my spreadsheets are xlsx files which were originally created in Numbers or OpenOffice that I just view and edit in Sheets. They remain normal files which immediately sync to my computer when changed. The rest of my data is a folder containing several thousand PDFs. So in my case I sync everything to my local hard and back up with Arqbackup.