> If you're using something like ECS or serverless, AWS gains nothing by optimizing the servers to make your code run faster - their hard work results in less billed infrastructure hours.

If ECS is faster, then you're more satisfied with AWS and less likely to migrate. You're also open to additional services that might bring up the spend (e.g. ECS Container Insights or X-Ray)

Source: Former Amazon employee

We did some benchmarks and ECS was definitely quite a bit more expensive for a given capacity than just running docker on our own EC2 instances. It also bears pointing out that a lot of applications (either in-house or off-the-shelf) expect a persistent mutable config directory or sqlite database.

We used EFS to solve that issue, but it was very awkward, expensive and slow, its certainly not meant for that.