An argument diagram shows the parts of the argument and the relations between them. This diagram does not say whether the argument is strong, weak, or even complete. It simply provides an accurate depiction of the parts and how they are related. That is the basic task of analysis. To give an analysis of an argument is very different from evaluating it.
Evaluation presents a value and judgement about the strength of the argument.
Analysis simply seeks to present the argument accurately. Analysis without evaluation is hard for many people to do. When we come across arguments that oppose our own beliefs, we tend to seek their destruction. When we deal with arguments that involve claims we agree with, we tend to overlook errors in their formation. The philosophical attitude is different from this.