"Why the Supreme Court Should Reject the Arizona Legislature’s Challenge to the Arizona Independent Redistricting Commission"

Not so sure. The power of the "legislature" to prescribe districts very well might include the legislature delegating to a commission or being subject to veto by a governor or referendum. Those are the examples cited. Here the people themselves initiated things. And, "legislature" is not the same as "legislative power." Cf. "executive authority" (17A). Tricky case that might turn on the congressional statute especially since Congress has its own power here.