I knew there would be people disappointed but I didn't think they're would be so many. The series has always thrived on unconventionality and the morally alien and warped values of the idaten and demons.
Miku saw the demons losing, so she ran away and tried to crawl back up. In the end, she's not about "winning" but choosing the best possible options given the situation. When they were the top dogs, tyrant empire. After managing to free the DK, it would have been that again if they won. However her 27 years were preparing for if the DK lost the final fight.
She's a good representation of a truly smart character. Sadly, the reality is that their end results will be boring.