You're (probably) not wrong about the abuse thing, but it sure is nice to just not care about that when you have fixed hardware. I find trying to guess which of the 200 aws services is the cheapest kinda stressful.
We're hoping to write a case study down the road that will give more detail. But the short version is that not all parts of the client's organisation have aligned skills/incentives. So sometimes code is deployed that makes, shall we say, 'atypical use' of the resources available.
In those cases, it is great to a) not get a shocking bill, and b) be able to somewhat support this atypical use until it can be remedied.
Why would it be abuse? Serving e.g. map tiles on a busy site can get up to tens of thousands of qps, I'd have thought serving that from S3 would have made sense if it weren't so expensive.
They specifically mention the dbt-core will remain open source and will be supported. However this type of consolidation will very likely bring increased prices.
I hope Fivetran alternatives like dlt remain open source.