As far as whether a dance is “easy” or not it comes down to a combination of things - the main ballroom/latin dances have a fixed syllabus of techniques that you have to follow and that is where you will hear the judges talking about things like foot positions, arm placements, etc being correct (or not), for other dances like Charleston, salsa, etc there is a much more fluid interpretation and whilst there’s a basic technique it is nowhere near as strict. Couples Choice is pretty much “anything goes” so it all comes down to how you sell it!
Rumba is NOT an easy dance! You could say it is marginally easier for the female celebs as they have more to do (the female partner - or “follower” if it’s a same sex couple) is the focus of this dance, the male (or leader) is there to show her off. But it is so slow! There is no room to hide if your technique or timing is poor - in a cha cha cha or a samba you can get away with wriggling your arse a bit to try and cover things up, but here it is all out on show. There’s a reason why so many celebs hate it!
Danced well, the rumba is a beautiful dance to watch. Danced badly, it is a horror show!