Massive bridges can make a BIG difference in the way an electric guitar or bass will sound.
I haven't investigated this to the extent you have, but I have a bass with a Babicz bridge and my sense is it supports what you say - more even response and much longer sustain. When I sampled it, I was determined not to loop the string and that often meant samples that lasted for over a minute before the level went under -60.
In your experience, does the massive bridge make more of a difference with bass than guitar?
There are so many variables. It partially comes down to rigidity. That which moves will vibrate, strings will transmit energy to anything that in proximity. Sometimes it's just a particular note.
An extreme would be a hollow body bass, most of them have notes that roar and notes that just sort of die. The result of a couple of specific resonant structure, the air volume in a hollow bass is tuned to a specific frequency. It may be random but it is there. Make the same hollow bass out of brass and I bet it sounds completely different.
I've noticed significant differences on guitars more often, I don't seem to work on as many basses. When I got the Schecter TriLok bridge and bolted it down solid on my 335 it transformed that guitar into a sustain monster. It still had resonances but they were more fun - easier to control.
I dunno, tossup?