The major issue out of the box vs any deduping backup software is that S3 doesnt support any deduplication. If you move or rename a 15GB file you're going to have to completely upload it again and also store a second copy and pay for it until your S3 bucket policy purges the previously uploaded file you've deleted. Also aws s3 sync is much slower since it has to iterate over all of the files to see if their size/timestamp has changed. Something like borgbackup is much faster as it uses smarter caching to skip unchanged directories etc.