Liberty is, by definition, a megaship. Quantum is only about 15,000 GRT larger and less than 400 pax more. If pax load is what you are using as a measure, Norwegian Breakaway (also considered a megaship) is more in line, but is roughly 23,000 GRT smaller than quantum. midsize is falling around the 100,000 GRT mark.
Not to mention, Odyssey OTS (quantum class) tenders into Grand Cayman as well.