I am talking about lounge singers with both companies. I sailed 8 out of 10 times with NCL on Jewel and Star class ships. I have not noticed a difference in quality of entertainers with RCI. They vary on both ships.
Also both have performers in theater. Production shows with dancers and singers, individual performers (pianist, singers, ventriloquist, magician).
Maybe problems on your sailings were connected to pandemics although in our experience cruises on RCI & Celebrity last and this year (7 in total) were full of entertainment.