The burden of proof is on Ivanov now. He can prove to the world he isn't cheating by performing that well repeatedly in tournaments where the arbiters are vigilantly working to stop cheating.
Either he will continue to play at that incredible level and
a) he is really as good as he says he is
b) he's found a brilliant way to cheat that can't be detected
or
His play shows that he was cheating.
I think everyone here expects that his play will deteriorate if he plays in any future events where the arbiters are vigilant. Kenneth Regan said that the odds of him not cheating are more than a million to one. Let Ivanov prove he's that 1 in a million.
I think the fundamental problem is you taking the cheater's side.
The burden of proof is upon the accuser, that's a pretty basic concept of jurisprudence.
That is entirely dependent upon which jurisdiction one resides within. The concept of "innocent until proven guilty" is not a universal legal principal. And what rises to the level of legal proof and facts of law differ from jurisdiction to jurisdiction as well.
However, even granting your point, we are not arguing before a tribunal or a judge. We are looking for sufficiently high quality proof to establish a probalistic determination.