Such a huge landscape of BI and data visualization tools. Are there any clear open source leaders? Apache Superset?

Superset and metabase are definitely the OSS leaders.

I work on an open source code-based BI tool called Evidence, which might be of interest to you.

It's effectively a static site generator aimed at building automated reports and analysis.

https://github.com/evidence-dev/evidence

Previous discussions on HN:

https://news.ycombinator.com/item?id=28304781 - 91 comments

https://news.ycombinator.com/item?id=35645464 - 97 comments