I think the reason that the wholesome content doesn’t come across as trite is because its main source (Ted) is depicted as a flawed man with positive goals. That effusive behavior on his part is a coping strategy that he has used to try to deal with his traumas, and while it may have had some success, it has also arguably harmed him and damaged his relationships. It isn’t saccharine to us because we can see that it isn’t something he is, but something he does. And because it is an action of his, as he grows and develops as a character, we get to see him changing his behavior to match his new understandings (e.g., his epic conversation with his mother).