Well, I like the term "authority". IMO, authority has more to do with the "presence" of an amp, than it does the tone of an amp. Presence is very hard to describe, as it is more of a feeling, or vibe, than it is a tonal thing. It's how the low end fills up the space around you and feels solid and supportive underneath your music. It's like your'e driving a big old bass locomotive and your band is along for the ride!
You can have two amps and EQ them to sound fairly similar, but the feel or presence can be the totally different. Your a/b test is a good example. Sure, the LMII may have "held its own" on a tone level, but I'm sure you noticed a big difference in the "presence" of the SVT, even with the Eq's and volumes set to sound similar. It's the 800lb. gorilla of bass and there is nothing really quite like the experience of playing one. Same with the DB750. It's just got this huge low end "presence" that goes a little beyond describing in a purely tonal fashion.