Not really. The existence of only single kill capable class, the limited yet common nature of the converts and the promotion system means that the 2 factions play very differently.
If the Cult had unique converts for every class, promoted the same way and had the same fundamental Kill rhythm as the Unseen then I would say they were too similar even if the converts and abilities were slightly different. But that isn’t the case, so its it’s fine.
While Prince is certainly better than Knight, that doesn’t make them the same thing.
Same goes for Knight.
Chronomancer doesn’t add anything to the game because they both stop the same things. When asking what they are used to deal with they are interchangeable.
However there are plenty of things Knights block that Physicians do not. That is why we can say that Knight is better against Reaper than Physician is but Possessor is better against Knight while Sorc can deal with Knight but not as well as Possessor and is weak to Physician.
The simple fact that Knight blocks things that Physician doesn’t and Physician blocks things that Knight doesn’t already makes them very difficult. Combine that with the fact that Knights guard is a counter attack and is also unsustainable in that it eventually Kills him too and they are only similar in that they stop Kills, which makes them comparable but not interchangeable like chronomancer and phys are.
As for the Knight CS there are important differences there too. Specifically CS visits, doesn’t bypass anything, and isn’t known to exist beforehand.
From the PoV of balance none of that is particularly meaningful, since they are all negatives besides the unknown part which is sometimes good (the REAL upside to CS is being unlimited use but that property isn’t important here).
This means Unseen/Cult have a bigger reason to worry about attacks (and thus can get converts to block said attacks), and they can also attempt a Kill on neuts for creditably. Neither of which are the case with just the Prince.
Hunters kills are either telegraphed or are too situational, Prince Kills are also telegraphed and are unstoppable anyways (making it pointless to try and get converts to stop it) and neuts don’t usually go for Scum, even NK’s.
Maid and Sheriff are about as similar as classes can be without being too similar (discounting classes with different wincons like alch vs phys) since they both serve the same overall purpose but achieve those functions in different ways with differing counterplay and considerations at any given moment.
Now what about this class?
Do we need a direct Kill? We already have the Knight, so what does it being here add to the game?
Technically a permanent convert block doesn’t exist, but we tried it before and it didn’t go well. Especially against the cult due to the stalemate potential. And up to 3 of these? It’s at best a balance hazard.
The only thing interesting here at all is a self frame. But a single interesting thing doesn’t offset the cost of having an unnecessary class in the game.
Remember, the more classes there are the more complex the game is. Which means in order to justify the class it needs to add more depth than it does complexity. Having classes that are fundamentally interchangeable adds less depth than classes which are not, but they both add similar amounts of complexity. So again, why should this class be added into the game? How is this supposed to improve the game? What interactions are possible thanks to this class that weren’t before and how do those interactions make the game more interesting?