That’s one of the reasons I used the word “primarily”, which is a word that I would defend. Even if many Americans don’t personally have much English descent, the shared cultural narrative of the country starts there. The central complaint of the American Revolution was that the British were infringing on our traditional “rights of Englishmen”, which evolved over centuries. We’ve retained the English language and the English common law. Many of our cultural and regional variations to this day, even down to our regional dialects, can be traced to those that existed in different parts of England.
Also, please find a reliable citation that says that more Americans have African than English heritage. That strikes me as a very surprising claim.
One consequence of American, especially historical, racism (including things like the one-drop rule) is that the experience, and over time the identity, of people (and thus their descendants) who were Black and something else tend to be heavily weighted on the Black side.
There are far more Americans who claim German descent than English. Irish, too. And Blacks.