Thank you so much for saying this!1. She is a secondary character. Her development stopped after the Sasori fight how long ago.. She is slightly more important than the rest of K11, but the Sannin trio/deadlock has been overshadowed by the elder-younger son struggle. Even if she was meant to be a main character, you cannot argue that she has gotten the same amount of spotlight as Naruto/Sasuke.
2. Sage chakra = physical + spiritual + nature energy. Not nature energy + chakra.
The yin seal can't help her attain a SSM if there is one, and if it does, Kishi will have
to change the rules about senjutsu, and seeing as frog sm and snake sm follow the same rules, I doubt it.
I've been saying the same thing (in this very thread) and people keep on shrugging it off.