I think the main thesis of the author was that Millennials are facing significant disadvantages compared to previous generations. For example, the baby boomers had Social Security, defined-benefit pension plans, a good economy most of the time, and life expectancy not much beyond retirement age, and a bunch of them still manage to be poor. Millennials might not have Social Security, are responsible for their own retirement plans, graduated into a shitty economy (which may also have significant challenges in the future due to peak oil and whatnot), and have to support themselves for 20+ years after reaching traditional retirement age.
Combine that with the author's other main thesis -- that, on average, people are too stupid to manage their own retirement -- and you end up with a lot of doom and gloom.