The Xavier arc in Legacy happened before Age of X. Since that arc in Legacy, memorable Xavier appearances could be counted on one hand. He and Legion joined the fray in Second Coming (you could say they turned the tide), and yes, Charles was involved in Age of X (which was a Legion-driven event). But since then he's more or less been off the X-grid, appearing more in the Illuminati than in the X-Men. When he got off the plane in AVX and was greeted by Magneto, I thought to myself, "enter the sacrificial lamb." And it turned out to be true.
But to my other point, Charles did get quite a favorable showing in this series - doing much better against the Phoenix (well, two halves of the Phoenix anyway) than he did during the Dark Phoenix saga. So at least it wasn't a Wasp-death or an Alpha Flight-death (respectively plucked out of a crowd and killed without a word and killed off-panel). Charles went out fighting, and will obviously be back.
Sorry, I wasn't clear... I know the Xavier arc was prior to Age of X but he was involved in the post Age of X Lost Legion story arc... although I do agree that he has generally been absent recently.