As a cultist and de facto leader thereof for the last couple rounds, the problems with the gamemode are manifold and coming from both sides of the equation.
First off, pubbies. In the recent Cult rounds, I've had starting cultists who took five minutes to locate their starting word after being told that they even have one, taking a foreverllion minutes to come to a place after getting two Communicate messages that it's urgent because they were buying toys from Axel, a guy who converted on the first try then immediately started blabbering about the identities of cultists and urging people to kill/arrest them, one of the guys above got Juggernauted and was just hanging around in the open, not to mention cultists asking about Cult mechanics in OOC in Secret...
Second off, meta. Dear god the meta. Chaplain, Heads and Sec being above suspicion by default. Security, upon seeing some bones piles and constructs gallops off to Chaplain, who immediately tells them every single meta-information about Cult (as in, information not based on in-round happenings, not specifically metagamey - like Engis knowing how to set up engine without experimenting with that), such as that they are TEH EVULZ, a group, and want to end the world and summon an evil god, despite there being no signs that a cohesive group was even working on the station - Sec ended up raiding.
Third off, recruitment has enough hoops to train a Dragoon Regiment if you don't go forceconversion route - you have to single out a person so nobody will lol off and tell on you to the redshirted teacher, make a pitch, hope said pitch succeeds or else the person will probably go tell on you except now will also use your pitch against you, then discreetly convert and equip them. And then people are reluctant to join, because they love their antag redtext for some reason, see 2). Due to 1) you have to do with, at best, two people who won't say 'BTW, we murder baby kittens for fun, I'm just gonna go throw myself in perma now.'