Just to offer my perspective (and leave it at that):
The line at the start of the story was intended to give a general reader with no sense of/interest in the Beach Boys a very quick, very broad outline of the arc of Brian's career before diving in. I consider it accurate: Brian did retreat, for many reasons; he was less productive and creative, especially after Sunflower, than he was prior to Smile; he did indulge in drugs; he did suffer from mental illness; and he has reentered the Beach Boys orbit more fully now than at any time since the late 1960s, with the possible exception of Love You.
Later in the article, I provided as much detail about the post-Smile years as I could afford to provide, considering my space restrictions and my general-interest audience. The one line I do regret writing was the one about Brian "usually" offering "only two or three songs per album"; that was meant to refer to 1971-1976 but sounds, due to some subsequent editing, as if it encompasses 1967-1970 as well. I will ask my editor if I can add a sentence or two to the web version about the Smiley Smile to Sunflower period. I love all of those records and they deserve to be included in the story.
NB: I do mention Love You and even Adult Child a few paragraphs later.