Most of these stories come from posters who have not stayed on that deck, we have had 13
DCL cruises and 11 on that deck, no issues.
The rooms on that deck both concierge and Cat 4 are the highest price of all rooms, why would people pay the top price if there was a serious issue?
Now I think those who post must be highly sensitive, yes if there is a pirate deck party and your room is directly below it, yes during the deck party you will hear something, it will stop as the party stops at 11 pm. I think some use this to imply the whole cruise is affected.
As for deck chairs running etc, well I am a very very light sleeper, I live in a quite location, I have good hearing, by company health checks say that, I have had 11 cruises on deck 8 of Nagic and Wonder, and the next is booked same location. Our cruises are long ones. There isn't any serious issue, the comments on the few posts are over exaggerated, please do not worry from Internet rumour, common sence that these rooms cost the most and sell out, tells you everything.
Other decks have issues, deck two near the engines and the vibration of the sea, under bars, other decks under entertainment areas, and rooms next to laundries with 24/7 noise, all cabins will get something, but deck 8 is fine.