Looker Studio wins when the data is small and the audience is large
A lot of Looker Studio reporting starts life in Google Sheets: someone keeps a tracker, connects it, and turns it into a dashboard the whole team can see. Add native connections to GA4, Search Console, YouTube, and BigQuery, plus free sharing, and Looker Studio is the cheapest way to publish summaries to many readers. It needs no warehouse at all, which Sigma cannot claim.
Where it struggles is scale. Performance drops on large datasets, and BigQuery-backed reports send a fresh query on interaction, so cost rises with every reader who clicks around.