Noah is, IMO, correct on this front. We aren't voting on what a person is but what a person will do. Someone who isn't a billionaire is no more immune to *influence* by billionaire interests. What we want is to see what politics a person will pursue, and how vigorously.
Remember the title to Brands’ FDR biography: Traitor to his Class. And his cousin Teddy, and JFK and his brothers, shared some tendencies in that direction as well.
Most non-billionaires politicians directly or tacitly argue for the continued existence of billionaires. Obviously, most non-politician billionaires argue for the same. What we're looking for are people who argue against that and, where possible, have political actions backing up that argument.