No, no, no,  

I missed the opening scene you so vividly describe, because I was hungry and wanted to eat a toast before the film. When i came in, Joaquin was sitting in the church, and the conversation with his family had seemingly just begun. In the end I thought i hadn't missed anything important, but now I believe I did miss the most important moment in the film. 

Anyway, it was clear to me that he adored his girlfriend, and the emotions came through very well throughout the film imo. I completely agree with you, that he would have needed somebody like Mann. The biggest gaps or "head-scratchers" for me definitely came throughout the police proceedings, but there were also some family scenes, and even the final discussion with Phoenix and Mendes, that could and sometimes should have been longer. 

Now I think I'll probably go and watch the film in German cinemas when it gets released. I have to see this first scene on the big screen. Hope the German synchro won't mess up the film too much.