MSC takes very serious the issue of Gluten sensitivity. My husband had the diagnose of having Gluten allergies before a cruise with MSC. We have informed the cruise line and he was served from a completely separated menu and with one person bringing his food to the table. They did everything to avoid contamination. It was a lot of effort from MSC because in case of a real allergy it can be life threatening. Fortunately a couple of months later another diagnosis for my husband found out that he did not have any gluten allergy. Unfortunately nowadays doctors are diagnosing this condition everywhere and it is not always the reason for the symptoms.
In your case you said, you are not really sensitive to Gluten but prefer not to eat food containing gluten. Maybe you could find out at the beginning of your cruise if that food is going to be available, for example because other guests do really need to eat gluten-free. In that case it might not be too much extra work for the cooks to prepare one more gluten free food for you. If there are no other guests with the condition, you might want to reconsider, for the sake of the crew involved in the cooking and serving the gluten free food, if you could not renounce to your preference for the time of your cruise. The crew at MSC ships work a lot and anything we could do to relieve them from additional work is a good action.
We try to relieve them from additional work for example requesting, that no turn down service in the evening shall be done in our cabin. It is nice to have everything fresh made when you return to your cabin, but we do not really need it. Just my humble opinion.
Ivi