I've noticed that there's no undelete/recycle bin function for PWA, so if you make any mistakes, there's no undoing (unlike Google Drive). This means PWA isn't good enough to be the sole backup, and additional backups should be made.
On that note, you can download all your files on Google using Google Takeout (search for it). It packages your files into 2 GB zip files. For PWA, some folders may be split into several zip files, but it seems ok - no files are repeated as far as I can tell.