Question about Harry Potter?

Firstly, we (the readers) got most of the info about the Elder Wand from a children's fairy tale book. The wand wasn't truly "unbeatable", but it was powerful. Secondly, Dumbledore wasn't just some frail old man. He was the most powerful wizard of his generation. Thirdly, the Elder Wand was a magical object. We all know that wands can change their allegiance, so there's no saying that the Elder Wand didn't do that. Dumbledore was the most powerful wizard, and the Elder Wand probably recognized that. If the wand traded allegiance before the duel was over, Grindewald had no chance.