I don't think this essay ever actually made the value judgment that doing "great work" is "the most important thing in life" or even a good thing in life. Did I miss that part? I read it as, "for better or worse, some people are driven to do great work, here are some techniques to accomplish that". I think it's true, right?, that such people do exist, whether that is good or bad for them.
I suppose I know enough of his history to know that he would make that value judgment, but I read this particular essay as being fairly agnostic about it, leaving it up to the reader.