I feel like I'm the only person who did not mind Nanamo's death being a red herring.

Its not out of any love of the character, but rather, the impact of what happened has not been forgotten. When the Warrior of Light is having dinner with Aymeric and Aymeric reaches for his glass of wine, you can FEEL your character tense up. Then there's the drastic change that happened in Nanamo herself as a result of this whole ordeal. She became a much better, stronger, less naive leader, and because of this, she was also able to free Raubahn to take up a leadership position in the liberated Ala Mhigo.

Nanamo's death had enough character developing repercussions (including one of the few we see our silent protagonists affected by), that I can't feel it was a bad choice.