While there's a lot to debate in the article, kudos to Graeber for talking about a taboo. White-collar employees 'work' (periods of focused concentration) a lot less than 40 hours. There are exceptions, and HNers may deny this fact (because the demographic is different or because the taboo is more powerful in this circle), but Graeber's inebriated cocktail party confessions match my own discussions with friends. Howe…
I am not going to deny anything you said, its almost 100% true. But I believe your missing an important "fact"(maybe). That is its not really physically/physiologically/mentally possible to put in 40 hours of true "work". Not consistently anyways. So as much as it is we not truly putting in 40 hours, its the entire effort to be available for 40 hours IMO that you are getting paid for.
However, for a lot of it I'm asked for help or input where my brain's called into action for a few minutes a time every now and again by other staff. We know this isn't productive for us, but if it provides value to the organisation as a whole (usually by solving something relatively minor, which is best expressed IRL than through the screen), then that's what they need of me.