What you seem to be missing is that you need one person alive and willing to prove that he's the owner of those private keys.
Since we don't have anybody doing that, all this soap opera has not much of a meaning. I'd say that this is the point you are missing.
I think even the proof that one is/was the owner of those private keys is not enough anymore. The more time passes, the higher the chances are for someone's privkey to collide with an already used one. While this is not a very likely scenario and the chances of colliding specifically with the genesis/Satoshi's privkeys are about zero, it's not practically impossible especially as tech evolves.. So if someone "finds out" 50 years from now who owned those private keys, chances are this is just a random coincidence and collision that proves nothing.
I could not agree more with you that an evidence and a witness may not be enough to prove that this claim is credible. It is right that as time passes by, and the longer the time has passed from the event, the difficult it would be to prove its legitimacy. And I must say that in situations like this, one witness account is not enough to be testified actually.