I think it is a good idea to add one of those mass builders in there. For one, with the romanian deadlift the hamstrings get worked from the hips, not the knees. This means you are working them completely in a different manner than with leg curl movements, even though both target the hamstrings. It helps with shaping the hamstrings and your glute-ham tie-in as well. I don’t think RDLs add too much mass to the bodypart it gives the illusion, which is important in bodybuilding. Sometimes the tape measure does not matter. It is all about the appearance.