Well, my understanding is that there's two major ways to use the coins - voluntarily or involuntarily. If you actively seek cooperation with the coin, you gain a high degree of control and power, but if you try to resist they may be able to seize control anyway - in which case you're just a vessel.
Am I mis-remembering that?
The various Fallen have their own various methods of getting the host to go along with their plans. Some are blunt and forceful. Others are subtle and tricky. While a voluntary host is more likely to gain power quickly, even an involuntary host can be forced or tricked into going along with the Fallen. After all, the forceful are incredibly powerful and have practice at breaking mortals, and the subtle are brilliant and have that same amount of practice.
This is part of what I was getting at above. Different hosts will combine differently with different Fallen. A patient, open, and unforceful Fallen isn't likely to get far with an unwilling host, but is likely to find fine partnership with a willing one. A trickster might get bored with a willing host, but be great at offering just the right power at the right time to an unwilling one.
A given Denarian is almost like individuality squared: You must take into account the host and the Fallen to some degree, and even that degree varies by Denarian.
So while what you way might be the case much of the time, some Fallen might render hosts into vessels whether they're willing or not. Some Fallen might never render hosts into vessels, far preferring the alternative.
