I thougth it was a good movie.. But all the things you mentioned where true..

I think the reason it was rushed is because they have to make the movies before the trio and everyone "Grow up" By the time the last movie is out it is said that Emma is going to be 20 so that means that Dan will be 21 and Rupert will be 22.. (I think if i got the ages correct. If not then correct me please)