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...the notion that sitting in traffic each morning to reach a room where one stares into a screen for 9 hours - every day, for 40 odd years - is desirable is the greatest con capitalism has ever pulled."
I think you're ignoring the biggest benefit of capitalism. While many people will do something fairly similar to what you're describing, it's not explicitly required or unchangeable. You have the ability, even if extremely challenging, to strive for better. For a person washing toilets, this could be the dream of sitting in front of that screen one day. For the person in front of that screen, it could be starting their own business or taking an early retirement and living the rest of their years off the beach.
Capitalism enables people to move up. The system you described would actually be perfectly reflective of a more social economic system like communism. The government would measure your competency and then offer you a series of jobs. You would take that a job off that list and you would do it til the day you were allowed to stop working. All without any chance for ever achieving something better beyond that list of jobs they decided you were qualified for. And of course you'd receive the same compensation when you're 18 as when you're 50 with decades of experience, because that's fair...
I think it would be phenomenally interesting to live in a pre-industrial time, just to experience it - but I suspect we'd quickly find that the tedium and unfairness of the systems we have to do would seem like utopia compared to the tedium and unfairness of those times. And so too can we expect people a few hundred years from now to live in what we would consider a utopia, yet themselves lack contentment striving for something better which will indeed come about a few centuries beyond. It's the nature of man to always strive for better and, at least to date, achieve it.