DO NOT underestimate the importance of a good academic transcript even if applying solely to dedicated art schools.
First, mainstream universities with top undergraduate art programs such as Carnegie Mellon and Yale, will indeed value your academic transcript as least as much if not more than your portfolio.
Second, so-called “academic art schools” such as RISD and Pratt, certainly take your academic record into strong consideration. Yes, I would agree, the portfolio takes precedence. However, with schools as competitive as these, I would argue that having the strong academic record may very well tip an admissions decision in your favor. The Foundation Year liberal arts courses at RISD are no joke and, in fact, are every bit as challenging as the AP/IB courses our daughter took in high school.
Third, but by no means least, $$$ MONEY $$$! Our daughter received many of the very generous talent-based scholarships described above. However, she also received separate academic awards that literally cut tuition by upwards of 75% in some cases.