This two-parter was brilliant and very fun to watch right up until it flopped dramatically at the end. For the first three-quarters, it was great. The AUs were cool (Sombraverse was awesome), the plot was interesting and dramatic, the tension was building, Twilight couldn't seem to win...and then Starlight reveals that this entire thing—her entire life, her becoming an evil cultist, all of that—was because her friend got his cutie mark before she did.
Seriously?
This doesn't make me feel pity for Starlight. It makes me feel like she is a brat who needs to be taught that the world does not revolve around her. Losing a friend, even a (supposedly) best friend—and considering how Sunburst barely looked at Starlight after he got his mark, I have a feeling this friendship was very one-sided—is not justification to brainwash ponies, hold them prisoner against their will, commit acts of violence, attack royalty, or try to change time just to stop a few ponies from being friends. Starlight isn't traumatized; she's petty and self-centered. Even if she truly is sorry, she shouldn't just get let off the hook like that. She needs to pay reparations for all the damage, mental and physical, that she has caused, in addition to being put under some kind of magic probation for several years or even decades. This is not a small quarrel between friends. This is not a slight misdemeanor. Starlight's actions were a capital crime. Even if she is truly sorry and wants to change (and based on her future behavior, i.e., brainwashing the M6, she doesn't), she shouldn't be allowed to suffer zero consequences. I am not looking forward to her appearance in later episodes.
Honestly, this art piece below encapsulates my feelings about Starlight pretty well:
TL;DR part 2 encapsulates everything wrong with the Equestrian justice system, and makes Starlight look like a childish jerk.