I was looking into this just yesterday. So the Loki + … comparison is a bit off in the Open Source space. The main ones are Signoz and ClickStack in this space. Both using ClickHouse as the database. Heavy compared to something like Loki, but they are OTEL native and not log monitoring. So not in the same category.
I'm partial to open observe, especially because in Ruby the OTEL stuff isn't great for metrics and logs yet.