Doing studies on this is difficult for many reasons. However, I bet there's a lot of people who noticed a drop in productivity from certain colleagues after the switch to WFH. I personally noticed that the productivity of colleagues with young children dropped significantly, for example.

I really don't think it's a controversial statement that some people work better from home and some people work worse from home. In fact, I'd be extremely surprised if the opposite was true (everyone works better from home, or everyone works better in the office), I'd almost say that's impossible.