I must admit that 'alternative' is always a tricky word... Datadog, Elasticsearch, and Splunk are giant beasts, and the alternative makes sense only on a subset of features (and hopefully, we will successfully execute our 2024 roadmap to reduce the difference)
For Quickwit, our users proved to us it was scaling up to petabytes. So we consider this scale factor in the "alternative". But... we don't have a dedicated metrics storage engine yet, so if you want to store metrics in Quickwit, it won't be efficient in the current version. It will come later this year.