Yeah I see people getting a flop and an underperforming movie mixed up. A flop should be considered as a movie that loses a studio money by not making back its production budget and marketing costs which would be Cats in this case. A movie that underperforms should be one that makes the studio back its money but doesn't meet the forecasted expectations and/or is projected to have a negative effect on future films due to not meeting consumer expectations which in this case would be the ROS.
ROS is projected to pass a billion but not expected to out gross the last jedi.