Yeah I have to agree, Joo might get lucky and throw off some other players, but he poses no threat to any of the the three Chinese players who might go. Even in his recent match against Boll, it was more a combination of Boll playing bad, Joo playing great, and thus pulled the upset, even with that, Joo only won in 7. In most circumstances Boll should win that match up.
Mizutani doesn't really pose a threat to Ma Long, but I think when he is playing well, and ZJK or Wang Hao are playing average, he has a chance to cause them a great deal of stress. I don't know how Ma Long would do against the apparently improved Ovtchov, but I don't see him having any really trouble. Despite Wang Hao actually losing to Ovtachov in the world teams, I think that match really should hold all that much weight in determining how they would do if they met up again. Wang showed he was more than capable in the world cup match, when the match is to 7. I think ZJK would have the most trouble against Ovtchov of the three, since ZJK's backhand, his main strong point also is Ovtchov's, so they match well against each other.
The three young koreans are unknown factors, because they definitely are really good, and the Chinese players haven't really played them that much, so they could be not use to their styles. ZJK already has lost once against one of them this year.
Its for these two main reasons that unlike many in this forum, I actually am not sure ZJK would be the better choice above Wang Hao to represent China.