I always wondered at the fan notion that the two idol groups are separated by lots of years. In my mind, they're three years apart. Both Love Live! SIP and Love Live! Sunshine existed for a couple of years before their animes, so SIP would take place around 2011-2013 and Sunshine around 2014-2016. That doesn't negate Dia saying Muse was "legendary" since 3 years is a long time in high school years.