The particular arrangement of The Fourth Turning is adamantly specific though (and quite famous in sociological circles, iirc it's where our modern concepts of "millenials" or "gen X" etc. come from); it's hard to mistake it for anything else.
I don't doubt for one second that Greene knows it, or that he'd expect a sophisticated audience (such as Googlers) to know it too — the credit is probably very much implied as soon as you present things this way. Like we don't need to credit someone for E=mc² or a²+b²=c² because it's obvious. Green is notoriously awesome at doing synthesis of a bunch of seminal sources, that's his M.O. — more than original thinking imho, but his delivery is often incredibly worthy of interest.
Fwiw, I'd argue it's extremely easy to take pretty much any social dimension(s) and slap some abstract model on top of it with relevance. I've read countless such accounts, and did it myself in regard to cycles in concentration of political power. Strauss-Howe's model is relatively interesting insofar as it draws upon quite long-term history (some variations / extensions go back to ~1200 iirc, though the core theory was fundamentally applied to the American civilization), which gives it weight.
Source: I studied sociology-anthropology-politics.
I think the future of social sciences is there, currently tightly secured intellectual property and datasets in the beating core of giant tech. Those who command enough of that elusive 'power' are now capable of shaping humanity to an unprecedented degree.
Like any tool, neither good nor bad but what we make of it...