So why did you continue to play all that time if all you were doing was exploiting a hole in the game?  Nothing better to do?

Post it under bugs.  That's where this belongs.

True.  The whole thing was obviously gamed from the start, a preplanned selection of moves that has the sovereign going out alone or in the company of beasts, elementals, etc.  It becomes less a game at that point than an orchestrated ode to oneself.  Not really a bug, in that sense.   More like exploiting cheese.

While this trick works, and is indeed extremely effective, I think that it is significantly less powerful than the quest loop.

At some point, I'll make a play-through to demonstrate the overwhelming effectiveness of the quest loop.  The strategy is described here.

I think the real issue here is the AI.  The AI is mostly a cookbook approach and cannot adapt to much of anything.

Here are some other ways to break it using magic+civilization:

build for population and spam huge sacrificial armies with low attack wearing thorns plus faction specific mechanisms for dealing with archers. I have not tried this yet so I am foggy on the details

build for mana generation and spam destiny's gift on your sovereign (pariden works best here, I think) needs cloudwalk and/or a bunch of champions and call of the titans (I once got Procipinee to 1000+ health and 200+ initiative, though this was long after she got a +4 initiative weapon and a similarly nice mount from the epic arena quest). And note that even if you never research destiny's gift you can still get the "battle is over before it starts" aspect using celerity. The mana requirements for this seem high, but once you're earning 300+/season that should probably count for something.

build for death shards using resolyn - blood sigil (and wither) means city militia. (and cyndrum demons, and your custom troops), etc. have high defenses, and again you can use your sovereign to capture all the cities with essences and wear down your opponent trying to take them back (I currently learning the ins and outs of this approach).

Each of these strategies has an achilles heel, I imagine, just like the classic shield wall + archer spam has an accuracy problem. But it is not clear to me that being able to walk all over the AI using massive power build up means that these approaches are buggy. By default you can win the game by killing a few dragons and such, or using a bit of research and construction and I think all of the above (along with others, like the scrolls plus shards approach) require significant additional work beyond what you need for those victory conditions.

That said, I can imagine stardock making some cheap changes on behalf of the AI if they cannot design for any of the paths that they feel they have made too easy or on behalf of the player if the AI using one of these approaches makes things too difficult.