Plot hole in Deathly Hallows?

Does anyone else wonder why Dumbledore didn't completely incapacitate Voldemort in some way at the end of OOTP? If he had this unbeatable Elder Wand, there's no reason for him to lose. Why didn't he cripple Voldemort to make things easier for Harry? Why didn't Dumbledore beat him before the first time Harry stopped him? It makes no sense. Mind you the wand was supposed to be unbeatable, and clearly wasn't if so many people lost it in a duel (Grindelwald to Dumbledore in the first place)