You're assuming this is the case. It isn't. Guests sing ALONG, not on microphone. With a good piano bar, the guest chooses their experience, from ambient entertainment to very inclusive, by where they sit. What happens off mic around the piano is a whole second level that guests on the other side of the rooom don't hear. The main difference is that at its heart, the dueling show as done on HAL was meant to be scripted, carefully timed material, so the screens would project trivia about what they're hearing. Solo piano bars may have a theme, but are ready to re-shape the evening, on a dime. Please note that there are dueling shows on other brands that are not scripted, and are nearly all requests. I do those, and very happily so, aboard NCL. Some great dueling is launching on RCCL. It's all what's right for the demographic present. In fact, on Day 1 of a new cruise, the stage manager or production manager would break down the cruise by age, location, and how many of each level of loyalty level are on board. This didn't affect most acts. But I would say, "Let's swap out Best & Worst of the 70's with Best of Broadway, and since we have so many Europeana, let's scratch TV themes and add in..." (and so forth).