The verdict
For ad-hoc analysis, modelling and anything where the shape of the question is still moving, Google Sheets wins , it is the most flexible tool either side of this comparison and it is the one you already know. For a recurring dashboard that needs to stay current, look polished and be shared without exporting screenshots every week, Looker Studio wins , it connects straight to GA4, Google Ads, BigQuery and 800+ other sources and renders interactive charts you would have to hand-build in a sheet.
The clean rule: if a human is going to edit the numbers, it belongs in Sheets. If a human is only going to read the numbers, it belongs in Looker Studio. Neither is a product-analytics platform , both report "false" on product analytics, session replay and heatmaps , so if you need event tracking or funnels, this whole pairing is the wrong shelf. For everything from MRR trackers to client marketing reports, though, the Sheets-feeds-Looker-Studio combination is hard to beat, and it costs nothing to start.