The only explanation that fits is that of Elder wand being crummy.
It's only extraordinary function appears to be that it will not work against its true owner.
In fact it will fly into their hand upon use.
Oh no hang on, it will work if you want to kill them and tear part of your soul out of them...
Has JK offered any explanation on the power of this wand? because, to me, it seems unusually woolly - as Hermione would say. It simply does what the story needs it to do, bit annoying really, as the rest of the magical lore is largely practical and logical.
Unfortunately there is no evidence of the Elder wand being more powerful than any other wand, as its only owners in the Novels (except Harry/Draco) are Dumbledore and Voldermort, both of whom are already disproportionately extraordinary.
Dumbledore must have just been better on the day.
Dumbledore should have allowed Harry to win it from him before burying himself with it. Might have made Harry's victory seem less like ridiculous luck. After all, he left very little else tochance.