I think there is some truth to this, but it doesn't particularly upset me. (Note: I was born in 1968, which puts me smack dab in the middle of Generation X.)
Part of it is simply that (as the author mentions) there are fewer Gen Xers to talk about. Raising children was a less popular undertaking during the 1960s and 1970s, as compared with either the postwar era or the child-obsessed 1980s and 1990s.
The Baby Boomers receive a lot of attention because they are currently in the retirement phase, and their mass exit from productive work has a huge impact on the economy, and their aging and eventual demise will impact demographics worldwide. In this context, it is worthwhile to talk about them in aggregate terms.
Generation Y's coming of age happened to coincide with the rise of the Internet. As we know, young people since time immemorial have been self-obsessed. They tend to believe that they are smarter than their parents, and their peer group is a source of great and unique received wisdom. (This belief is almost always incorrect.) So the result is that when you look online, you see a lot of young people engaging in what can be described as self-obsessed, narcissistic behavior.
I was self-obsessed and probably narcissistic at 18 or 25, too. But there was no Internet back then, and so there was no platform for me to broadcast my narcissism to the world.
People born between 1964 and 1980 are today between 50 and 34 years old. In other words: they are middle aged. Retirement is somewhat interesting to talk about, and everyone enjoys talking about youth. But the travails, frustrations, and compromises of middle age? Not so much.
Another important point from the article:
"They [Gen Xers] are less likely than Millennials and Baby Boomers to think their generation is unique, and they don't have as firm a view on what makes them special."
I agree wholeheartedly with this one. Many of us (me included) were only children and key latch kids. In the 1970s and 1980s, there was less emphasis on group activities for children in the after school hours and during summer vacations. So on average, we tended to spend a lot of time alone. (Kids today, by contrast, are chronically over-scheduled.)
Growing up in small families with a lot of alone time made many of us individualistic, suspicious of mass movements, and cynical. This certainly describes me, and I believe that it also describes many of my contemporaries.