If Plumlee is doing everything Keene is doing, there wouldn't be a competition at this point. I don't think the players and staff is blind to the fact that one QB is significantly more athletic and has a better chance to improvise. On top of that Plumlee was recruited by Malzahn, fits his style of offense more.
More likely the reason why players/coaches feel its close, Plumlee isn't running the offense as well because of various reasons (rust, knowledge of playbook, accuracy, ect.) so its not a cut and dry decision.