I have been on both the Adamantoise and Brynhildr NN for quite some time, and they aren't nearly as bad as your time in the NN has been. The two worst things that can happen is it turning into a general chat, and the large amount of mentors vs small number of sprouts. I can't say how these issues can be fixed as I'm feeling out of it and not willing to type a paragraph more, but I feel getting rid of the crown and thusly crown cravers would help alleviate them by reducing mentor count in the NN.