This is literally pre-play prep. I'm not trying to be argumentative but I'm really not seeing how you're claiming this is not prep. It uses a different system from D&D and is more collaborative but the general premise is the same.
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it is still pre-prep in that system of the same type you would do to prepare for a D&D game
The general premise has almost nothing in common.
In Gygax's explanation in his DMG, in Moldvay's explanation, in the 5e example of play in the Basic PDF with the keep and the gargoyles and so on, the general premise is that
the GM has written up some setting in advance and then starts describing that to the players, thus prompting them to declare actions. In both Gygax's and the 5e example of play, some of the earliest declared actions are requests for more information (by inspecting things, poking at things, etc).
Perhaps I've not described In A Wicked Age with sufficient clarity, but no one does anything before the group sits down to play their session. There are no GM maps or notes. There are no secret NPCs, because all the characters have been listed by the group as part of the "interpretation" of the Oracles. There are no actions of the inspecting things, poking at things etc variety, that oblige the GM to reveal more of what they have prepped.
I find it hard to think of anything more different from how D&D and the role of prep is presented that still counts as a RPG.
Ok I have Agon 2nd edition... and form what I remember... The GM preps an island, that is afflicted by some type of problem. There is an initial conflict when the heroes arrive... exploration of the island with a focus on the overcoming of the issues the overarching problem has caused and a climactic battle. This is all prepared beforehand, and there are lists of pre-prepped islands in the actual book. Does it specifically have lists of monsters... no, but it has pre-prepped items of it's own (mainly islands, npc's, problems, etc.).
There is no "exploration of the island" in Agon 2e as there is "exploration of the gargoyles" in the 5e D&D example of play. The Agon procedures of play are pretty clear. The Strife Player presents each island—its strife, opponents, and other characters—by
revealing the situation, asking leading questions, and judging contests. Agon quite closely resembles, in this respect, Dogs in the Vineyard. But not 5e D&D-type prep.
Unlike DitV, it has a more stylised sequence on each island: Arrival => Trials => Battle. Exploration doesn't figure there.
The Keep on the Borderlands and The Village of Hommlett have NPCs with problems etc - that's pretty standard fiction - but as far as play is concerned they are a type of puzzle for the players to discover or unravel (like, who's the spy? is the friendly priest really a friend? etc).
Contrast Vincent Baker on how to reveal the Town in DitV (pp 138-9):
The town you’ve made has secrets. It has, quite likely, terrible secrets — blood and sex and murder and damnation.
But you the GM, you don’t have secrets a’tall. Instead, you have cool things — bloody, sexy, murderous, damned cool things — that you can’t wait to share.
There’s this interesting hump I have to get over every time I GM Dogs — maybe it’ll go away eventually. It’s like this:
The PCs arrive in town. I have someone meet them. They ask how things are going. The person says that, well, things are going okay, mostly. The PCs say, “mostly?”
And I’m like “uh oh. They’re going to figure out what’s wrong in the town! Better stonewall. Poker face: on!” And then I’m like “wait a sec. I want them to figure out what’s wrong in the town. In fact, I want to show them what’s wrong! Otherwise they’ll wander around waiting for me to drop them a clue, I’ll have my dumb poker face on, and we’ll be bored stupid the whole evening.”
So instead of having the NPC say “oh no, I meant that things are going just fine, and I shut up now,” I have the NPC launch into his or her tirade. “Things are awful! This person’s sleeping with this other person not with me, they murdered the schoolteacher, blood pours down the meeting house walls every night!”
...Or sometimes, the NPC wants to lie, instead. That’s okay! I have the NPC lie. You’ve watched movies. You always can tell when you’re watching a movie who’s lying and who’s telling the truth. And wouldn’t you know it, most the time the players are looking at me with skeptical looks, and I give them a little sly nod that yep, she’s lying. And they get these great, mean, tooth-showing grins — because when someone lies to them, ho boy does it not work out.
Then the game goes somewhere.
The remarks about "being bored" and the game "going somewhere" are remarks about DitV: it is not a game which has procedures for "dropping clues" and the players finding them. (Contrast, in otherwise quite different ways, both Keep on the Borderlands and Trail of Cthulhu.) For a game of DitV to go somewhere, the GM has to reveal the problems, not make them objects of discovery. Agon is the same.
This is a very different orientation to prep from a game like the one presented in that opening example of the 5e Basic pdf.