However, S3 isn't trying to replace your NAS. S3 offers many use cases where it is the smartest and most viable solution. The most common use case is as centralized block storage for an online web app, that runs on load balancers, a CDN, and distributed servers. If you run an app that is going to run on multiple servers and get load balanced between them, then uploading directly to the servers is complicated. Since a user could upload something to server A one time, and a month later they could request the file while visiting on server B, C, D, E, etc. This centralized S3 platform simplifies the block storage for these large apps.
S3 does offer more advanced features as well that many people aren't educated on. For example, S3 Lifecycle Management allows you to set up timelines so that your file uploads are available on S3 for 30 days (when users are most likely to access them), then automatically move them to reduced redundancy (reduces cost, but at lower 99.9% SLA) when the file is 30-120 days old, and after that it moves to Glacier storage (long term, taped storage, super cheap), for long term storage when it is unlikely to be retrieved but needs to be kept. You can also set up a CDN just for this block storage, with over 200 edge locations all around the world.
S3 also offers HIPAA and PCI compliance. There is also incredibly robust user management (Through AWS IAM). Plus you get 11x9's of availability (99.999999999% availability).
Im not trying to sell you on S3. It definetely isn't for everyone. There are times when I would tell people that it isn't a good fit. But if you work on enterprise apps, it gives you a lot of enterprise level features for month-to-month, (relatively) straightforward pricing, no long term commitements, etc. Which is something that doesn't generally exist in the world of enterprise software or PAAS (which is what S3 really is). So for that, S3 is a breakthrough product.
S3's biggest flaw is its price. If you are using all the enterprise features than it is arguably worth it, especially considering the 11 nines of availability. But for anyone on a non-enterprise app that doesn't need that stuff, there are far cheaper solutions out there for you. Blackblaze B2, Wasabi, Digital Ocean Spaces are three that come to mind.