I know this is a very unusual comparison but suddenly this thought occured to me.
People call Janak hi as Videh since he never got emotional, all his decisions were always neutral and never did he ever have a bias. But still he got emotional when Sitaji was married and was leaving for her in laws place.
VedVyas ji on the other hand exhibited the biggest level of neutral behaviour. If we look it logically, then Duryodhan and Kauravs were his biological grand sons. Pandavas were not related to him by bloodline since they were not the biological sons of Pandu.
He had to write the story of Mahabharata so that we might know what happened, the story of Mahabharata as we know is what he told us. Couldn't he mould the story to make Kauravs as the defeated heroes? They were his biological grand sons as I said and they did have their positives too as much as they had their points to prove them rightful. Had he got his emotions while writing Mahabharata, he could have got slightly biased towards his blood lineage, but he remained neutral and to such an extent that he made his grandchildren the biggest villains of Itihas for time immemorial. Till the time Sanatanis remain on this earth (although going by current trends I don't think there would be much time) his grandchildren will remain the biggest villains of Itihas. Not just that, he never approached Dhritrashtra and Pandu as his sons (something like Indradev Vayudev and Suryadev etc. Often did) because he knew that they might have his blood but they were the Kshetraj children of Vichitraveer ji. Even he didn't have extra emotions for Vidurji despite the fact that he didn't have any father of his since he was born while performing his duties
Don't you think that his level of neutrality was actually much greater than Maharaja Janak? Wasn't he the Videh in real sense?