Not sure I'd say Royal Caribbean is 'quite a bit pricier' than Carnival, but they are often a little more expensive.
I've encountered rudeness on other lines. We had a rather pompous maitre'd on the Celebrity Mercury several years ago who came around the tables making it pretty clear he expected to be tipped. Well, as a result of that I didn't give him a penny and on the last night he made a snotty remark to me as I left the dining room.
I also saw a bar supervisor publicly berate a bartender because a passenger had just complained to the supervisor about what she felt was being 'dissed' by the bartender. He did this behind the bar while passengers were all around it. Totally unacceptable conduct by the supervisor. What's more, the woman had spilled her pina colada and the bartender gave her a free replacement, but without the fruit garnish. She was upset because the drink didn't look pretty and went looking for the supervisor. This was also on Celebrity. Note that Celebrity is considered a premium cruise line.
And, I've seen crew who were simply having a bad day now and then - on Royal Caribbean too. They can have a personal problem which clouds their judgment, perhaps they were chewed out by their boss, didn't get enough rest, forced to work extra hours, etc. I am not excusing the conduct, but just saying there can be a reason for it.
Personally I have never had bad service or any smart remarks from any Carnival employee. But I have seen times when they were just going through the motions of being a happy employee.