I was on this same sailing and yes, you said it well. What appeared to be the majority of people on this sailing, were large tour groups from other countries and although the behavior they were exhibiting is considered totally normal in their countries, it is rude loud and inconsiderate by American standards. As others have stated, it definitely made a difference on this cruise in all of the dining areas, shows and public areas. In over 50 cruises, I can say that our fellow cruisers on this ship/sailing were by far the most challenging.
With that being said, I found that a lot of this could have been avoided if the crew would take control of some of these areas. I have sailed on most major lines and this was my first MSC cruise. The crew on this ship just didn't seem to manage or care when it came to stuff like this. The best example is the main theater. Every show I attended was the same. The crew would scan cards to make sure everyone had a reservation but once the show started, it was a free-for-all. Passengers just kept walking in, talking at full volume as they tried to find seats for their parties, standing in the aisles blocking the view of those seated and this went on for the entire show. There were also kids sitting in the aisles and as kids do, they were not sitting quietly, enjoying the show. Then there were the cellphones...they were on everywhere with people holding them up high in front of them recording and taking pictures.
I have never seen a theater, on land or at sea, that was so chaotic and there was not a crew member to be seen anywhere. Needless to say, the shows were not very enjoyable.