Okay, so I'll break this down one step at a time. The claim that spell card duels are done with a "bet" in mind is a gross misrepresentation of what's actually said. The
SCR draft makes no mention of this.
Reimu's PMiSS article does mention it (as does the more up-to-date version of the spell card rules,
from SCoOW), but you might find a
very slight issue in how it's phrased:
"Agreed upon
before the duel". No terms are made with Eirin prior to fighting her. Nobody says "if you lose, you have to remove the corridor"; In fact, they directly ask her to dispel the illusory moon she created, and
she says no. But, you may argue that this deal just happened offscreen, so I can objectively prove that the protagonists did not ask Eirin to remove the corridor. In the
Barrier Team's scenario, Eirin has to explain where they even are and that the corridor was endless, accentuated with Reimu's "??" showing she genuinely does not know where she is (after all, she was only following Eirin). This happens
again in the
Magic Team route, with Eirin even commenting on how they don't realize where they've ended up. And, of course,
Youmu's response is one of "false passage? huh?". So let me ask you this: How can these characters ask Eirin to dispel something
that they do not even know exists?
They literally could not make a bet with Eirin to remove the corridor, because they didn't know it existed until they had already crossed it. There's also the logical issue of
when they encounter Eirin; They actually do so at the end of stage 5,
before they enter the corridor. Now, Eirin's goal here is to trick the protagonists into entering the fake, infinite corridor so they don't find Kaguya... so, if they make a deal when they first encounter Eirin, why would she reveal that one of the corridors is fake to begin with? It would render the entire deal moot, because the protagonists could just go "hey thanks for telling us one of the corridors is fake, dumbass",
except they obviously don't do that, so its clear that they only learn of its existence after they cross it.
And now I move on to the idea that they crossed the corridor at the exact same time, or by chance. Saying they crossed it at the same time is uh, nonsensical? Partly because I can't understand why this would disprove infinite speed, and partly because I don't even know what that means. If it's in regards to both protagonists reaching the end at the same time, then that doesn't work, because they're deliberately traveling in a pair to work as a team. If it's in regards to them reaching the end at the same time as Eirin, then that doesn't work because
Eirin is leading them there and they're just
chasing after her. If it's in regards to the stage taking the same amount of time for each character... uh, yeah, that's how STGs work. They're basically on rails, which is why you can't really go faster or slower on any given stage (the only time variance lies in how long it takes to kill bosses/midbosses). Every possible interpretation I can give your claim doesn't hold up to scrutiny, which is almost impressive.
As for Eirin or Kaguya dispelling the corridor... Eirin has no ability which would allow her to do that. No power null, no infinite range space-time manipulation, no nothing. She can, at the very least, ask Kaguya, right? She is a
telepath, after all (something I overlooked in my prior response). Except... nothing even indicates she does this, and doesn't even make sense with your theory; The protagonists don't even know Kaguya
exists. They'd be asking Eirin to ask someone they're completely unaware of to dispel the corridor (something which
they don't even know she can do, by the way), which means this entire argument boils down to "after we beat you up in the infinite corridor we choose to go down for no reason (because you just told us about it), could you please telepathically call your friend we don't know about and have her use her hypothetical ability (which we also don't know about) and have her dispel the corridor? Also, can you explain what the corridor is several minutes
after we beat you?" vs "THEY GOT TO THE END BECAUSE THEY FLEW THERE". It's a rather simple case of Occam's razor.
Also, asking Kaguya after you beat her makes no sense. You don't fight Kaguya at all in stage 6A (the route where the feat happens); In fact, you never even encounter her in a form besided a disembodied voice telling Eirin to get back up and fight. And when you
do fight her in stage 6B, that's when you choose the real, non-infinite corridor, so... what would the point even be?
Of course, even ignoring the logical holes, the misrepresentations, every tiny flaw in your argument, there is one thing that objectively cannot be overlooked: That this is wholly hypothetical, and has no solid evidence backing it.
The space-y background you see is actually an illusion. So where are they if not in space? Well, Heaven. The sealing spell Eirin put over the earth has its borders in between the earth and Lunar Capital (it
is meant to separate the two, after all). The distance between the earth and Lunar Capital is stated to be Heaven on multiple occasions; Yukari has to
chart a path through Heaven in order to reach the capital, the capital views Heaven as geographically beneath itself, and Koishi outright says
Heaven is what lies between the earth and moon. Heaven is, well...
infinite. So the "end point" of the corridor is an undefined distance away from earth, being at the midpoint of an infinite distance. This means the only reliable way we can scale the corridor's size is via... the statements pertaining to its size, every single one of which (all 10+ of 'em) says it's infinite.
The corridor is not an illusion. Literally the entire premise of the story is that the youkai (and Yuyuko) can
see through Eirin's illusions; It's why they notice the moon is missing to begin with. So why would they not be able to tell the corridor was an illusion? Furthermore, this is
directly contradicted twice; First in ULiL, where it's shown that the corridor is a spell cast by Kaguya that
infinitely links together pieces of space-time (not an illusion), and in CDS, where it's stated that
Kaguya's abilities are used to create the infinite corridors (said abilities being the manipulation of the eternal and the instantaneous; also not an illusion).
Not exclusive to the Lunarians.
CDS confirms the corridor is there to deter
any intruders, not just Lunarians, and
ULiL has Kaguya break out the infinite corridor spell in response to intruders that are Definitely Not Lunarians. Both of these happen well after they realize they're not under attack from the capital anymore, too.
Route B is irrelevant, the feat doesn't even happen there (the Eirin in route B is a fake, anyways, so lmao). You are right about route A, though. Let me post her dialogue for convenience's sake.
Okay, so she has no reason to dispel the corridor. She is literally
trying to prevent that from happening (assuming your theory about them "betting" to dispel the corridor on Eirin's defeat is even true). This is completely incongruent with your interpretation of events.
Bro you literally have
hard evidence saying Kaguya made it, what do you MEAN "assumption"??
The ship is directly compared to a
bullet train, which travels to its destination at top speed without stopping or slowing down. Furthermore, the ship was already spotted flying through Gensokyo well before the protagonists caught up to it; It had literal
hours to build up speed, so it was almost certainly at top speed by the time the protagonists started chasing it.
Uh, no, the "I won't let you cross!" is just a way of saying she's going to stop Marisa. It isn't an acknowledgement of speed, it's just... saying you are going to stop someone from doing what they are currently trying to do. This is a very weird reading of a pretty common turn of phrase.
Okay, this is COMPLETELY ignoring the context of the feat. Whether or not the fee applies to living humans
does not matter, because the protagonists do not pay the fee when crossing it in WBaWC.
They even lament the fact that they didn't pay the toll, because doing so would've made their trip more convenient.
Furthermore, countless beast spirits are also crossing the river, and not only are they not alive, but they are literally a
hostile force invading Gensokyo - They have no reason to pay the toll at all.
FWIW,
Chiyari also crosses the river without paying any kind of fee in UDoALG.