Oh great ! Another lover of castles! We will be able to discuss at length the defense systems, the strengths and weaknesses of our drawings!
As for this one, you are absolutely right: this arch is only there for decoration, it has no defensive role. I judged that the defenses were sufficient until this stage of progress (to reach the city, we still have to cross the bridge, which seems to me as well defended).
If you like castles, you can also make a return on this
drawing. There are several flaws (partially forgotten) in the defense of this castle ...
Otherwise, I read that you lived in Switzerland? In what part of the country?