If you want to look at it that way, sure. But Michael, Sanya, and Shiro all have Knight of the Cross as their High Concept, and another aspect that relates to their swords. That supports the argument that they still need to take an aspect for their IoP.
It would probably make things more clear if YS gave more IoP examples than just the swords, but I'd say that the Musts for the swords are in addition to the Musts for the IoP power.
It does limit the narrative more, but IoPs aren't like other abilities. They can be loaned out, and offer a massive discount on power cost. I think they're intended to be major focal points of stories.
Of course, your High Concept could be "Bearer of the Holy Spear", and that's fine. Knights of the Cross are different, though, I think, going by what's presented in YS and OW.