As with anything, there are tradeoffs. There are situations where S3 is cheaper. For my use case (long term storage, rarely downloaded), Glacier Deep Archive is about $1/TB/mo which is cheaper than anything else out there (rsync.net, Backblaze R2, Cloudflare R3, Wasabi). Where you get bitten by Glacier is if you need frequent access since you pay a fee for AWS to retrieve the file in addition to the bandwidth used to download it.