I stopped reading early, when the article said that in the 1970s one big relational database did everything.

In fact, relational databases did nothing in the 1970s. They didn't even exist yet in commercial form.

My first prediction as an analyst from 1982 onwards was that "index-based" DBMS would take over from linked-list DBMS and flat files. (That was meant to cover both inverted-list and relational systems; I expected inverted-list DBMS to outperform relational ones for longer than they did.)