I disagree, since we know Sakurai doesn't need sole popularity to include characters. Some character additions literally are "Sakurai picks" through and through. But that doesn't matter with the base game, since people will buy that anyway - even if it has random, "WTF" picks like
, it still has popular Smash fanbase requests like
, or just characters with notable popularity within the general Nintendo fanbase like
, so people still buy the base game.
They said the whole point of the ballot was to get in characters the fans want, which would more than likely entail the majority rather than the minority. Also consider that the characters they pick are a product that will be sold on it's own, not with other characters. A lot of people only want the characters they like, so it is within neither Sakurai's/Nintendo's, or the fanbase's best interests, to pick characters that have little popularity in the fanbase.
So yeah, I think the ballot is as close to being a popularity contest without them explicitly saying it is.
That's just how I see it though, because I don't think the existence of the ballot makes sense otherwise.