Well, there's an argument to be made that captains of industry shouldn't own newspapers, full stop. That argument can be made without evidence, and there's some credence to it.
When someone comes up with a profitable model that can support real, independent journalism, perhaps we can start making that argument. Personally, if I compare quality journalism with a blind spot for Bezos, neo-nazi/alt-right crackpot "news" sites and small-town Romanians making up fake news to go viral on Facebook, I'm inclined to think that what little bias WaPo has isn't really that big of a problem.