The article doesn't claim that we are worse off for the more adolescent, individualist culture. Just that it poses unique challenges, especially in its excesses and pathologies.
Moreover, it explicitly makes your point:
> The phrase ‘unintended consequences’ used at the beginning of this essay usually implies negative effects, but there are notable benefits as well. .... These youthful character traits have served to make us more accepting and generous in many respects. Rising tolerance towards marginalised groups can be partly attributed to this emergent youthful mindset
Evidence is indeed lacking in the article, but the author is clearly writing against a scholarly background that almost certainly provides mountains of evidence and analyses, quality notwithstanding. Complaining about evidence in a context like this is like one of my friends in high school who went through an obnoxiously cynical phase, exhorting "prove it" after even the most prosaic, non-substantive statements. (I think he had just begun dabbling with philosophy, including epistemology. Or maybe I had and was also obnoxiously regurgitating philosophical claims in other conversations.) This is not an academic paper. It's an essay summarizing some themes that the author and others are investigating--or at least analyzing. And while making some rather concrete claims[1], it abstains from specific, substantive judgments, conclusions, or prescriptions. Personally, it's only when I see the latter that I begin to scrutinize arguments more closely. Otherwise, I understand these essays as merely providing a window into discourse that hasn't yet gone mainstream, and I mostly look for rough coherency. Whether I agree with the claims, let alone the premises, is an entirely different matter. But these essays can help you anticipate socio-cultural memes and identify potential evidence, both confirming and disconfirming.
[1] Specifically, the linkage between high school socialization and culture. Which, IMO, is an interesting thesis I had not come across before; one that is much more concrete and falsifiable than typical Golden Age-themed lamentations; and one arguably in the vein of the Hajnal line hypothesis[2] in that it links particularized adolescent social patterns to broader social phenomena and evolution. By contrast, mere observations that modern culture is increasingly adolescent are hardly new. The TV show Seinfeld parodies and even satirizes it, albeit without ridicule or negative judgment. Compare It's Always Sunny in Philadelphia, which uses similar satire, except the themes are less subtle and the writers and actors admit to substantively critiquing contemporary culture.
[2] https://en.wikipedia.org/wiki/Hajnal_line