We have quite a few Carnival sailings under our belts, with a fair # of Royal cruises (on the Allure at the moment - 3 night!). One place where Royal shines (on Oasis and new class ships) is the suite lounge and Coastal Kitchen. Even though we have in the past, I don't see us sailing on any prior class of ship with Royal. Kind of the same way I feel about Excel class on Carnival.
We presently have the Utopia booked for later this year (again, a 3/4 night Oasis class ship!) and then the Star for '26. The Star is nearly $2k/per person for a 7-nt inside (not what we booked), so it's a significant premium.
A comment was made about the passengers -- when we left Pt. Canaveral yesterday, the (Carnival) Liberty left on their 3-nt as well. We've sailed on that very itinerary several times, and hands down you can tell a difference. Everything else being equal - and in general - on Carnival you're going to see a difference in how people perceive "Cruise Casual" attire. You're also going to see more undesirable behavior (language and such). Again, each sailing (on any ship) will have variances and unique characteristics, but there are baseline differences nonetheless.
Tom