Allow my to present a slightly different view on this matter. To start with, know that I am going to tip on a cruise ship (and other places) and the only question for me is as to the method by which I tip.
Yours is a comparisson of RCI and NCL. We cruised both lines when "tipping envelopes" were used. We always found RCI to have the best service compared to NCL. So there may be more factors than tipping mechaincs at play here.
Some of the so-called "lux lines" have tips included in their higher fare. Everybody tips, or they don't sail! On the other side of the coin, the service crew there are paid better than if they were on a ship with separate tipping of some kind. They had the best-paying service crew jobs on the seas, and they wanted to keep them. As a result, we found the service under this system to be the best we'd experienced on any cruise ship.