If you (royal you - anybody who wants to make this claim) really want to claim that many people are measurably more productive at the office, we'll need studies to counter those done which show WFH is more productive than working from the office.
I think some people _are_ more productive WFH. But also there are lots of people who become quite unproductive WFH. Direct managers can often tell.
I don't know of a study that says one way or another, but from experience those two kinds of people exist (among other kids of people).
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.