S3 is great and in fact, at Transloadit we deploy a content ingestion network (reverse cdn) of many regional tusd servers, close to our customers’ end users, but they all ultimately save to S3 using multipart. We’re happy S3 customers.

So why the extra layer. Because this let’s us offer resumability below 5MB, lower regional latencies, roll our own auth, and switch to a different cloud provider without introducing breaking changes at the customer facing side (assuming the new cloud bucket provider does not offer an S3 compatible interface, or even just a slightly incompatible one)

Ultimately you’re still locked-in with AWS protocol-wise, and there’s no community platform for advancing it, so addressing any of these issues is going to be hard.