You can make change desirable, it just has to be seen as positive and healthy change. I mean, in a story, seeing a character you love die off can come across in multiple ways. It can easily come off as a “that’s a jerk move from the author” or come off as a truly tragic moment. It’s how you present the change that is critical.
Proper character growth, even for a villain, can be welcomed. So long as its believable and makes the character more dynamic and interesting. A villain growing and developing and becoming logically more powerful can make a good story even better.
However, when characters suddenly gain power and it feels like a “yeah, I just took twenty levels in Necromancer, which breaks the level cap by the way, because the plot demands it” of course people are going to be less than pleased.