Love these kinds of design stories, thank you!
If I may ask, is the live balance team usually greatly concerned with keeping a champion’s original theme intact during gameplay, or are practical solutions for balance way more of a priority for them?
As someone who used to work on that team, and still works closely with them—theme is definitely a consideration. The team always tries to keep theme intact (or even enhance it where possible), though the work is often all about trade-offs in the end because no balance change is going to be perfect and they all cost something to someone.
I will say that if any change is going to more severely undercut theme, the mandate will often be to find another way to get the job done, because theme is clearly an important part of our champions.