This relationship between employers and workers (the bourgeoisie and the working class when writ large) is one of the essential elements of capitalism. -- article

Capitalism requires the bourgeosie to exist, since it requires private ownership. But the relationship between them and workers is absolutely fundamentally irrelevant to capitalism, which I suspect the author knows.

It's a book review not an article with an argument to make. The concluding paragraph makes no claims:

"This book isn’t a book of answers; it is a book of questions and discussion resulting from those questions. The only certainty one might derive when they have finished reading it is that the only chance we have in defeating the ongoing march towards greater catastrophe wrought by human subjugation to capital is to be found in the struggle against capitalism and in organizing that struggle."