Nothing is wrong with Wu, just rank doesn't mean you are pro. I've seen a field general beat a Chariot gen in a 1v1 mock full flask. Pretty weapons don't mean anything if you can't use them well. Sure you might do a little extra damage, have some more hp, or be able to take another hit or two, but it means nothing when you are bad with it.
The reason the Chariot underestimated that field gen was because of rank, but the field general pretty much mocked all day when they played. The chariot did arena farming all day. So when it came down to battle experience, the field general had much more.
All in all, don't ever expect someone is good because of rank, the only way to know is by actually playing with him.