It seems more ridiculous to me that the game could end and I could lose even if I have 100 (summoned) models fighting on the board.
I suppose that you absolutely refused to play the
Blood & Glory pitched battle in 8th edition, then? After all, you can lose the match even though you've only lost, say, a single unit of 10... despite having 100+ models on the board. There is nothing ridiculous about a game delegating an abstract victory condition like that - plenty of games do it. It wasn't ridiculous for that to happen in 8th, so why is it ridiculous for AoS to do such a thing?
This is compounded further by the fact that 8th edition had no "benchmark" choice - you had to either roll before every single game, or discuss it with your opponent and choose one of six. Because of this variance (different players want different matches), is it unrealistic to suppose that AoS's current "benchmark" is similar to blood & glory? We'll know more when the big book is released, I guess.
"no enemy models left on the field of battle" is a pretty simple condition to check for.
What does "destroyed its foe" mean?
"In the Mortal Realms battles are brutal
and uncompromising – they are fought to
the bitter end, with one side able to claim
victory because it has
destroyed its foe
or there are no enemy models left on the
field of battle."
You've focused a lot on the 'no enemy models' thing, but could this be handled by 'destroyed its foe'? That's wide for interpretation, and one of my biggest curiosities in all of this. It seems that there are more than two ways to get a major victory (table opponent/Sudden Death), by that language.
If "destroyed its foe" doesn't mean sudden death (few objectives involve destruction, all require models), doesn't mean killing all enemy models (that comes after the 'or'), then what does it mean? Are they clarifying "destroyed its foe" with "no enemy models"? I have my doubts. They read as separate thoughts. The latter isn't placed in parentheses, it doesn't follow a comma, nothin'. Is this to be handled as "Blood & Glory"?
If I summon a model and it does not count as "my model", then whose model is it? If it's not "my model" then I can literally do nothing with it:
Actually, the rules are pretty clear that summoned models are "added to your army."
"Models
added to your army during the
game (for example, through summoning,..."
They simply don't count for tallying up models, which brings me back to my original question(s)... if you lose 100% of your army (remember, summoned models don't count here), what happens? Do these models cease belonging to any army, as the army's existence depends on starting models? Would that not end the game in a way that "is not obvious"? Is this any different than "breaking" in Blood & Glory? Would your opponent have not "destroyed its foe"?
If you are trying to use the rules that "models added to your army during the game do not count towards the number of models in the army, but must be counted among the casualties an army suffers." for any purpose other than calculating the winner of a minor victory then I think you are you are attempting to WAAC more than those that understand that rule to apply narrowly to the minor victory calculation.
I just wonder if this is how they meant to balance 'sudden death + summoning' lists in the same way that Blood & Glory put down players that didn't bring standards/fielded MSU in order to min/max.
Attempting to WAAC? Dude, I'm posting in an online forum, looking for clarity - nothing to lose, here. I'm not playing against anyone, nor would I force this idea (or any idea) on any of my opponents. I'm not trying to dick over my opponents just so I can say that I'd won. So you can rest assured, I guess.
Anyway, I imagine most games are gonna be prefaced with a talk about summoning, because practically every other player that I've met or otherwise encountered has had valid questions about it.
Where do you see the language which ties that paragraph specifically to minor victories? It appears that it can apply to major victories, depending on the meaning of a few phrases. I wonder about "or if the outcome is not obvious," too... that also seems to be a separate thought.
@hdctambien , you've got a pretty nice brain! I'm gonna keep prodding it, if you don't mind.

I could care less whether someone decides to plop down a Slann, summon their entire army, hide Oxyotl and piss of their opponents. That's up to them. I do, however, still have questions about this rule. I e-mailed gamefaqs, though I doubt I'll get a response.