My suggestion is simple.
Remove conversion entirely from the unseen faction.
Give them 4 starting members, no recruiting. Let the mastermind fulfill a different function
Bold, I know. Might sound crazy. But I think the current design is bad.
For a start, very few really like conversion. It’s a terrible mechanic mostly. You’re enjoying the game and then you get ripped out of it and forced to suddenly adopt an entirely new mindset. Getting into character once is hard enough, doing it again midgame is pretty jarring, and many people simply fail at it.
Second, there’s already cult. They do converting. Why do we need two factions that revolve around conversion? It makes the two not feel very different from each other.
Thirdly, and perhaps most annoyingly to my mind. It seems like you - the developers - don’t like conversion either. It’s getting gradually chipped away at. Sheriff scout, Wizard’s Clear Mind, and now the king’s fealty ability. Not to mention dividing the previously convertible mercenary into two unconvertible classes.
All of these changes over the past months have had the net effect of making the Mastermind play experience worse and worse and worse. Greatly increasing the chances that a conversion will fail, for one of many reasons.
It leads to frustrating games that are highly luck based. You can’t just pick someone you want to convert, any revealed person is likely to be protected against it. Often you just have to pick a quiet target and pray that they’re convertible, useful, not afk, and can suddenly adapt to being a new class. And that their converted class isn’t one that’s immediately proveable.
I think converting is just not fun. For most people, in either faction
I’m not saying all those corrupted class versions need to go away though, just swap the unseen from a conversion based strategy, to a strategy based on using their initial numbers. Give them a starting party of Mastermind, Asasssin, and two randomly selected corrupted classes.
As for the mastermind themselves, give them a broad array of investigative and hampering abilities to make them a useful asset. And more significantly, to allow them to convincingly fake a broad variety of roles