That's not a universally accurate assessment. It all depends on the nature of the work, the nature of the on-site work environment, and the nature of the at-home work environment. (among other factors).

I have significantly less wasted time working from home. At work, if I have 2 or 3 meetings in a day, that day is practically wasted for other work between walking to the meeting (I work on a large multi-building site), waiting for everyone to arrive, etc. Then it seems like people never want to end a meeting until its scheduled stop time even if we're done after 20 minutes. Then I have to get back to my office... Zoom has changed all of that. Zero time wasted at the beginning or end, and people don't seem to have as much of a problem saying "all right that's all we have, see you later" and ending a meeting early.

I can also get a bit more sleep in the mornings because I don't have to get ready to leave the house, commute, park, get to my office, etc. When the end of the day comes, I'm already home, giving me an automatic hour of extra time each day. You can do a lot with 5 more hours of free time each week. I get to see my kids for more time, especially my youngest, who I watch, as my wife oversees distance learning for the other two.

Even with the added distractions of working with at home with kids present, This past year has been one of the most productive in my entire career.

I'm sure that mine is neither a unique experience, but also not how it works for everyone else. But the mindset that says it's mostly more productive to work on-site is why some places ban WFH, as mine did before the pandemic.

I do, however, agree that WFH is least likely to result in the same or higher level of productivity for junior staff.