When it comes to drama, emotional honesty can overcome an awful lot.
anime director JC Staff got Ebara Masahi (Hideyoshi from Hyouge Mono, Van Hohenheim, Alastor among many, many iconic roles). He instantly brings a gravity and presence to that minor role that's so crucial to this little drama. And then there was the choice of Hirano Fumi (Keito from Tsuritama) to play Gouda, the veteran seiyuu competing against Azuki for the role of Naho. The notion of having a 57 year-old actress play the role of an actress trying out for the role of a high-schooler is fascinating on so many levels - hilariously self-referential, cuttingly satirical, and very witty. And I have to give it up the wonderful Hirano-san - when she launched into her Naho voice, it really felt as if 30 years (I can't quite give her 40) dropped off her.
20 contestants that was much more interesting than anticipated, I think the fact is that Bakuman figured out the only possible way this could possibly work without feeling like a complete asspull - they had Azuki win over the audience for exactly the right reason. It isn't simply that Azuki knows "Reversi" better than anyone - it's that Naho is Azuki. That's why Azuki should be the one to play her irrespective of her connections - she understands the role in a fundamental way no one else ever could. Like all Ashirogi's female leads, Naho is a love letter from Mashiro to Azuki. And so her factual familiarity played a role, in her catching the Weiss/Schwarz mistake in the script. And her innate familiarity played a role, because she brought out the depth in the character the way none of the other candidates did. So when she won by a landslide (among 191,228 votes cast!) it didn't seem cheap or contrived - instead, it seemed like the only possible outcome.