Your story is actually a great example of why Nutriscore is important. It showed you with a single letter that something you thought was good for you, is not.
Most people are uneducated when it comes to the nutritional value of food, and it can be very hard to compare similar food products. We added nutritional details on packages years ago, with little to no effect. The positive effects of the nutriscore were seen in the first year (better buying practices from buyers, brand adapting food content to get better grades, …)