Most stuff produced in the 90s was also formulaic slop but there was more visual diversity back then at least. Probably because there were more studios with their own styles while today there are a handful of big corporations that have monopolized the industry. Formulaic slop happened when traditional cel animation was abandoned. Coincidence? I don’t think so. If you walk into a studio you’ll see most of the animators use the same tools and rely more on their tools than animators of the past and the bosses are slave drivers who want them to produce as many episodes fast as possible.