the key is Reduced rotating weight. A standard UST tubeless tire is heavier than the corresponding non-tubeless version. But Chuck, you are right, once you allow for the heft of the inner tube, the weight is usually a bit less. (If you add sealant, your weight is about the same, or even slightly more.)
Many tubeless riders, including myself, actually use a standard tire on UST rims with tire sealant. This can shed over 100 grams per wheel.
This reduction of "rotating weight" makes the bike "zippier." It accelerates better, corners faster, brakes faster. <--- This is what I immediately noticed. again shedding that rotational weight is like shedding 3 times that on your bike.
you'll know what I mean when you go for that first 2bliss ride. ..... i couldn't wipe the smile off my face that first 2bliss ride. simply awesome!