It doesn't matter so much that Voldemort didn't see the exact means of his downfall coming. What bothers me most is that he was sloppy.

The point of my post is that I am much less intelligent than Voldemort, and vastly less experienced in cunning and subterfuge, yet I was able to think of a dozen relatively practical means of reducing risk from Harry in 20 minutes. How many would Voldemort have thought of and implemented if he'd tried?

Maybe they wouldn't have worked against the actual solution Harry chose. That only makes the story better. It means Harry successfully defeats the Voldemort we know and love, Voldemort at the top of his game, not a cut-down Voldemort shacked by a sudden Idiot Ball.

A satisfying way to defeat Voldemort would take advantage of his genuine weaknesses - his despair in humanity, his loneliness, his arrogance, his inability to comprehend genuine compassion, his need for a worthy foe. But until the latest chapters, he had not been shown to have the weaknesses of carelessness, poor planning, or leaving a dangerous enemy armed when they are in his power.