I haven't been on all the RCCL ships, but I don't recall adult-sized water slides on any of them. RCCL would seem to have a corporate policy of not having slides. RCCL is all about the rock climbing walls! And the skating rinks! And the FlowRider!
My experiences with water slides have been with Carnival, and frankly I've found them to be a problematic attraction. They are closed more than they are open, long lines, water splashing out and onto unsuspecting passersby, and they sometimes have to be closed because of winds. And finally, people do get hurt in them. I strained my neck during a run in the slide on the Carnival Pride.