Some Chinese pro said:

There is no best DotA player. There is only the best DotA team.

ZSMJ in the rape era. He got such good protection from the rest of his team (who were the real game winners) that anything other than huge farm would have been poor.

reply...

ZSMJ was very well protected by his team and he had amazing supports, but as his peak he was an extremely reliable carry player.

And that's the most important part of carrying - reliability. I don't remember him doing any mistakes that cost his team the match at the top of his game. And that's quite hard to do, you have to keep a cool head and focus. Look at Xboct - good carry player, but I can't even count all the times he died due to overextending to kill a support hero.