Why are we suddenly considering extremes and Savages midcore? Will Ultimates be midcore next?

Because that's what the lead battle designer said in an interview: “During the 6.x era, we received a lot of player feedback regarding a lack of midcore content, as well as a strong desire for more large-scale content. The chaotic alliance raid is our direct response to these requests. With that in mind, we decided our target audience would primarily be those who fall somewhere between extreme trials and the first two savage encounters.."