While China has the sovereign right to make whatever leadership changes it wants without having to explain the reasons why to the public, it’s also a Great Power with global influence whose decisions have a major impact on International Relations, hence why these shake-ups prompted speculation from many.
"...the best-case scenario is that Qin and Li were dismissed for corruption-related reasons..."
I disagree. I think the best-case scenario is that China is an adult in the room reaching for innovative, but carefully considered, strategies to manage the moods of the children with whom they've been compelled to associate. See, e.g.: 'https://wehavekids.com/education/Behavior-Management-Strategies-for-Kindergartners' and/or 'https://teachingwheart.com/10-proven-strategies-for-classroom-management-in-kindergarten/' for relevant detail.