Oh, ok, now I understand! Flagship = whatever book come out first. No matter that there nearly always was 2 main teams of X-Men, one in "X-Men" (or "New X-Men") and the other in UXM. A new 3rd book that is created and that doesn't have anything to do with those 2 main books is suddenly the flagship and replace them. Ok. Whatever.
Scott, Emma and co were already in a book before Bendis UXM. And it was already planed that Bendis would write UXM before he started writing ANXM. It was not about one book supporting the other: it was 2 different books with different concept and different "mood". One that had nothing to do with the previous story arcs and characters involved in them and one that was directly following up on the conséquences of AvX and the P5.
What Bendis said is that he doesn't claim the idea is from him. That it was already floating around. But he was the one that wanted to write a story based on this concept. Now you are free to believe that Marvel told him: you shall write a story about the O5 or you are fire. It doesn't change anything: It still didnt "stole" the "rightfull" place of another book.
Because you said that ANXM and UXM are the reasons why the sales are going down. X-Men had nothing to do with them so it should have sold better.
O5 minus Jean but with X-23 and at least 2 of the JGS kids. And you said it yourself: it's the third book. The one that didn't replaced X-Men or UXM but was an extra book based on the O5.