Ryoma will go on to be the best not just because he is the main character but because he evolves during every match. Fuji never showed his full potential until the match with Sharishi. Tezuka always comes out with something new not really evolving during the match, there are not many players who can make him go all out. That being said, Tezuka and Fuji do have their limits while Ryoma surpasses his limits all the time because that is a part of his play style and personality.
Look at how good Ryoma is without the Pinnacle of Hard work or Wisdom. I know some people didn't like the match between Ryoma and Atobe but thats because they dont like Ryoma. But that match truly showed what Ryoma was capable of without any of the doors to MUGA.
Oh well, people favoring certain characters over another is nothing new. It all comes down to who you like and that is who you most likey will favor.