It's funny how people have this perception...I have been on the Dream with 3,500+ people and on Oasis ships with close to 6,000 and have felt that the Oasis ships feel WAY less crowded than a full Disney ship. The ships size and design lend a lot to that. Yes there are more people, but the ship is MUCH bigger, and (at least on the Royal Ships) they do a great job with their neighborhood design to make sure people are spread around the ship. Any time you get everyone on the ship in one place at the same time, any cruise ship will feel crowded.
Just because this ship is big and has 6000 people doesn't automatically mean it will be more crowded. I personally would love to sail on an Oasis-sized
DCL ship. They have so much more room to work with. A common complaint of the Wish is venues are so small, people can't get into Palo, the trivia venues get overflowed, hallways are too narrow.
If anyone has been in Mickey's Mainsail on the Wish, you know what I am taking about. Making the ship wider can fix a lot of issues with space in common areas.