You would never get me on a ship that size. It would be good for the "cruise ship is my destination" cruisers.
One problem is infrastructure overload. For example, Skagway has a permanent population of less than one thousand. The last time we were there on a ship, a Carnival ship was also in port, dumping about 6,000 on the town.
Also many ports cannot accommodate a ship that large. That leaves out almost all tender ports. Imagine how long it take to tender 9,000 cruisers?
Santorini has a problem now, and they are limiting the number of ships at one time. The cable car to the top only handles 36 people at a time!