I think the point the author is trying to push, is how artistically boring the Edo period was compared to the vibrant late-Muromachi and Azuchi-Momoyama era. Sure, there's the rinpa school founded by Koetsu, the nanga and then also ukiyo-e, but the most important schools were Kano and Tosa, who were considered boring and uninspired since they produced "official" art.