She should have wanted to kill herself
Now that is nihilism.
if she had actually reformed.
Nope. The desire to live so as to right wrongs is also a legitimate manifestation of changing for the better.
It was a silly storyline for a cartoony Space Hitler character that never really got their punishment for all the atrocities committed.
And from a narrative standpoint, she literally sacrificed her life trying to make up for that before being rescued by
You can argue how well the narrative intent was executed (because there is a level of subjectivity to that), but your original critique that Mirror Philipa was never horrified by her previous actions is just false. She was horrified, and she tried to right the things she had done wrong, and she died in that alternate timeline for it.
One time is enough. Obviously it's not worth engaging further with material one does not enjoy.
Which is fine, but you should separate the question of your enjoyment from the question of narrative functionality. The former is completely subjective; the latter is not, yet you keep making critiques based on inaccurate assertions of the latter.
Interesting how that was received so much better as a satisfying serialized payoff, than the crying Kelpian child being responsible for The Burn.
Not that interesting. There's a segment of Trek "fandom" that would respond to DIS walking on water by snickering and saying, "Can't swim, huh?"
For myself: I lost my mother very shortly after DIS S3 aired. And I absolutely defend the revelation that the Burn was caused by Su'Kal's grief. If my grief could have burnt down the galaxy, it would have. It was a good creative decision and I don't want to be friends with you if you mock it.
Who else determines whether it is good?
Time, mostly.
Some works are popular when they were created and then endure forever -- most of Shakespeare, for instance. Some works emerge in obscurity and then achieve lasting love later on -- The Great Gatsby and Moby-Dick. Some works are popular when they emerge and then are forgotten -- Jan & Dean, for instance. And some works are unpopular when they emerge and stay unpopular -- the infamous 1987 bomb Ishtar, for instance.
The Last Jedi also lost about 700M in potential box office (compared to it's predecessor) due to poor Wom, diminishing returns.
Citation needed.