My idea for the hostile hosting thing actually mirrors a seizure much more closely - it all depends on how much crosstalk the humans produce. A trained human knows how to produce deadly amounts of crosstalk for the spirit to make sure it can't do whatever it wants and also ruin its structure in the process, while an untrained one wouldn't, and would only moderately (variably) harm the spirit in the process, especially if the spirit (a practiced spirit, of course, who has been exposed to this sort of risk many times) jumps in for an instant to simply twist the right thing all the way around, then jump out. And it is much easier for a spirit to kill a human than it is for a human to kill a spirit, hence why humans scarcely ever (unless they have spirit partners to put them back together afterward) survive hostile hosting.
The whole point of the belief thing is to make the spirits more alien, render their mentality and physiology different from humans. So far they're intangible humans with powers, largely mentally identical. They're not really terribly alien at all is what I'm saying. There's no meaningful gulf between the average human and the average spirit, and no, being weird-looking and unfamiliar with human culture (if even that) is not a very meaningful gulf. As for spirits remaining naive and suggestible their entire life, consider that a human being is naive and suggestible their entire life as well - you just need to know the right buttons to push, the right impulses to exploit. Hence, con artists - everyone can be conned if they're put on the spot and manipulated quickly from an unusual position (being immune to con artistry is only possible by carefully avoiding any such setups, which for the spirit wouldn't be entirely practical). It's not even always a matter to make them genuinely believe something is their weakness - it's to make them forget for a moment that it wouldn't be, and when the contrary is witnessed, it makes it part of their role - if they didn't recoil from it later, they wouldn't be very consistent, would they? Especially to themselves. A spirit's interest above all others, I envision, is to stay in character as much as possible, and their superior control of their bodies allows them to stay in character to a physiological level humans can only begin to approach.
And no, they can't really be wrong about themselves - part of the hosting thing I wrote about may have mentioned the entropy thing - spirits constantly change in contact with the world, and the template helps them remember what they should try to be and return to, and prevent long-term deterioration and eventual non-viability. The template is remembered - it's not a constant thing kept consistently, and you can convince a spirit they have been wrong about themselves, and their body would then change accordingly as doubts about the template crop up and are resolved. Spirits have no objective means of keeping their information straight, and even human partners help matters only a little bit. Thing is, they just plain forget a lot of things over time. Or misremember them. Or even manufacture memories to fit their internal narrative when the original memory is unsalvageable. Just like humans, in fact, though a human still finds the idea that spirits do it unnerving. You could even have spirit memory be far less efficient than human memory, only being reasonably accurate for, say, up to ten years ago, if they were existent then (and fabricated before their existence if they weren't), or even less. The rest they've either fabricated over time to fit their template and better explain their current situation or just plain forgotten - their memories, much like their bodies, are chaotic things.
Finally, as far as I recall, the MiniLuv scenes were brainwashing, not a wordless an actual argument. Psychological manipulation through words, being put on the spot, a person being removed from their context and then reshaped as needed with appropriate stimuli. The process was wordless because if it wasn't, it wouldn't feel very effective in writing - I imagine quite a bit of words and other meaningful forms of communication were traded in the process. But I might be remembering it wrong, was some 6-8 years ago when I read 1984. I'll go dig up the quotes and see if that helps me understand.
EDIT: Okay, read the last part of 1984 again (entirety of Winston's captivity), and I fail to grasp how anything similar could be done wordlessly, on the spot, and with connected minds. Wordlessness you could assume to be explained away through mental overlap. But doing it on the spot is absolutely bollocks - it's a highly involved process, molding any mind in such a manner. It requires a strictly controlled environment (which does not occur in field conditions), powerlessness on the victim's part (the spirit is decidedly not powerless in practically any circumstance), an unassailable dominance on the captor's part (if a mind is revealed to the spirit, then it doesn't seem likely, unless the human intellect in question is much more alien and frighteningly dogmatic than that of the spirits themselves, and even then the minds would overlap, as they occupy the same space, where you can't draw a line between one and the other), and also time (which hosting does not permit). It's just nonsensical, and not even vaguely applicable. You can't systematically deconstruct identity and reality in the span of two minutes, or five, or even ten. It just doesn't work.
The hostile hosting thing, as I thought of it, was essentially spirits being able to mess people up really badly if they meld into them, and the best purely human answer to it being mutually assured destruction attained through training that discourages spirits from doing it all the time. The practice itself may have developed from the single paranoid and lucky son of a gun who wasn't killed while resisting - for maximum irony, maybe this was because the spirit was trying to help him the entire time without his consent. He then passed on the knowledge to others before trying it on a hostile spirit (presumably years later) and killing both it and himself in the process, though by that point the idea is firmly established in anti-spirit lore. Since then, maybe one or two spirit-unaided people have ever survived the process in even a vaguely viable state. In some cases, the idea of sacrifice being needed may have planted itself into spirit-killer minds (compared to, say, the average spirit-hunter who'd be content to just make a spirit go away and stop whatever it's trying to do, and maybe get paid for it afterwards).
Bluffing, unlike what you describe, is much more impulse-based, and works much better in an urgent situation. It depends on the heat of the moment, and actually kind of makes sense and is possible to do consistently and write convincingly (because mental grappling usually comes down to a literal mind-wrestling contest, which is much more obviously silly than the idea of trying to argue with your own mind why it shouldn't exist, which is only more ludicrous the longer you think about).