Shalashaskka: First off, thanks for the reply!
I would argue that while the paths certainly differ in their details, the general plot does remain the same: each background pushes you towards the Ziggeraut for one reason or another. You're still required to visit the cities and speak to many of the same NPCs and find a way to the temple. Even the endings where you don't decide the fate of the sarcophagus directly (i.e., the God ending), you're still required to travel to one of the end game locations and follow the story path there.
So while the faction-based paths do differ - and very radically - the main McGuffin is static between them. At least from what I've played/researched.
True, but there are many possible variations that alter the gameworld quite drastically.
SPOILER
e.g. it's possible that at least two of the cities in the game can be totally destroyed as a consequence of your actions.
I can't really think of any other game that offers so many different outcomes as Age of Decadence...maybe Fallout 1/2, but even there choice was more limited imo.
Anyway, I didn't mean to nitpick...you've made a good review, and I'm in agreement with much of it.
