Hi @tt2lh.
Although the two services offer similar interactions I do think they offer a similar service. Distinct difference:
- Timestream offers a way to update data and Cloudwatch does not.

- Timestream has a JDBC connection API, making application integrations easy.
- Unsure about the specifics here. But the timestream storage layer is built for scaling out on application use-cases. The use-case of Cloudwatch is different here. So I can expect a difference in the quality of service there.

- I believe the query API of Timestream is richer (however it's difficult to do a full comparison on docs)
- Downside for Timestream might be that it has fewer native bindings for libraries.