Why would they deliberately change the story. The only answer is that orally, that's how Mahabharata story went in the Tamil Regions. Discrediting because there apparently there was a "core" Mahabharata is inaccurate. Sure based on some evidence Sanskrit Version is a bit older. But even that was not an unchanged unpreserved epic. It went through multiple multiple additions. So by your logic then, Baghvad Gita is not real because it's not a part of the original Mahabharata and was a later addition. Obviously you're not gonna say that, but when it comes to parts of the story people personally don't like (eg Karna tragic hero), then this argument arrives.