No, you don't. A plot's overarching structure is a thing in itself. The scenes it consists of are irrelevant in that respect (but they are both relevant to the story and experience as a whole), and we certainly have that information.
And no, you don't need an entire plot to judge a plot structure. That's kinda the point. We know how the game is split up, thus we can judge the overarching structure. Perhaps the plot itself might be harder to judge, as the structure is but a part of it, but there is no need to "wait judgement" anyways, as you judge things on what's available, not on what might hypothetically later be known. We don't know about the plot's pacing or all the scenes, which is the only part where "30 hour game" is remotely relevant. That's without considering that it's a game and likely filled with a lot of gameplay in those 30 hours, which again is irrelevant to the plot.
To give you an example:
humanity discovers impending doom thanks to scientist
scientists builds a AI driven computer DNA hotel "louis" and an ark
deteriorating hotel 1
deteriorating hotel 2
louis malfunctioning
ark returns to earth after millions of years and saves the hotel and start bringing humanity back
It can even be used in the same format as we know from TLoU2:
humanity-doomed
2-solutions
hotel-built
humanity-dying
20000-ad
1200000-ad
louis-flashback
ark-returns
That's the overarching plot structure of the one shot manga "Hotel". Sure, the story is more than its structure, but that's not what's being judged. What's being judged is the structure of the plot and the plot beats connected to them. It's not about the depth, because Hotel has a lot of depths and interesting aspects and scenes that happens within that structure. That's also why I've said that TLoU2 might be better than its structure, just like TLoU1 was. The problem is that the structure of TLoU2 and the story beats connected to them are awful, especially in the context of its predecessor, unlike TLoU1 which was more typical or generic.
It tells us more than enough for us to judge something like a timeline or a structure. That's also how the whole field of history works, by analyzing pieces of history and making casual and analytical judgements of them. If you combine screenshots and videos into it as well, then suddenly you have a plethora of information to judge something based on. Then once the game comes out (ie. getting more information) you can reassess things, though something structural is unlikely to change much. So your defense here is pretty weak. It's not like it's a rumour, we have actual information about the structure of the game. Literary analysis focus on all of these different things, though that's usually in a descriptive way (basically picking apart every aspect of a story) and not prescriptive as I'm doing.
In TLoU2's case we know the basic overarching structure and we even know some of the important story beats. Thus we have lots of things to judge the plot on without having to experience it all. Sure, we can't judge the whole story, because the story as a whole is more than the plot, but we have enough to be able to say "that's bad". Introducing the daughter of a no-name surgeon from the first game and a revenge plot is also as a story beat, especially in the context of the first game, that just is awful. Then again, perhaps there's so magical missing link that somehow justifies the choice of structure and story beats. However, you're arguing too much in its favor, saying that because we don't know every single thing about the game, that somehow there's something there that'll make things better, when in fact the opposite might be true, that it might make things much worse. What we can judge is what we know and that should be what's the most important, not wishful thinking about what might be, which is akin to religious fanaticism.
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