Well, yeah, but that's part of the legend that grew up around the wand, that it was "unbeatable". It wasn't really, no more than Harry's Invisibility Cloak could really hide him from Death. The wand (when it acknowledged its user as its true Master) just conferred a *lot* more power onto the user than did the average wand. But the user could still be distracted, caught by surprise, etc., as Dumbledore was. He was surprised by Draco, and had a split-second choice to defend himself or to protect Harry by keeping him out of the fight. He chose Harry, and so was "beaten" by Draco. Not the wand's fault, and I suspect that the wand "chose" to acknowledge Draco as it's true Master because Dumbledore didn't use the wand as the wand would have expected (i.e., to battle an enemy).
In the end, it still boiled down to the wizard, not the wand. :P
no more than Harry's Invisibility Cloak could really hide him from Death Remember Mad-Eye could see Harry through his cloak, so it wasn't quite as perfect as the legend claimed. One of the unanswered questions of the epilog is whether they ever went back to recover the eye and give it a better burial, ideally with whatever was left of Mad-Eye in the aftermath.