It's an open secret that we have no idea how to actually measure tech company productivity. That's why there isn't and will not be clear evidence for or against RTO.
Best you can do is pick a narrow enough sliver that it is measurable. Then claim it is the "important" view and wow, what a shock, the data supports your position!
I agree on an individual level, but at a company level it’s fairly easy to measure things like product feature shipping velocity, change in business metrics like growth etc. When you’re talking about company wide changes like RTO it would theoretically show up in these core metrics.