I'm not sure about which ships you've experienced but we recently sailed on the Rotterdam after numerous cruises on the S-class ships and I largely agree with your observations. We found the MDR on the Rotterdam to be unbelievably noisy. I think this is due the relatively low metal ceiling in the MDR on the Rotterdam with very little sound adsorbing material to be seen. We normally have Select time dining on the S-class ships and that is on the second floor of the dining room with higher ceilings. We really like the most forward areas on the S-class ships, they are a little more separated from the MDR and tend to be quiet. In contrast, the first-floor dining areas on the S-class that are located under the second-floor dining areas, have relatively low ceilings and tend to be noisy, very similar to the Rotterdam.