From my opinion, the cult of planet is one of the weakest factions (the cult and the pirates). The cult get +2 planet and -1 industry -1 economy. They get a brood pit free
with centauri genetics (a very far tech) and get mind worms to do double police units.
First, why to get police units with mind worms when you can get, for much less minerals and free of support, clean police scout infantry?
You can indeed capture mind worms, which can be good at the beginning. But the thing is you've got to be lucky so the mind worms you'll capture won't be supported by an early base and cost you one mineral each turn, unless you put them in fungus (wich is absolutely useless for police, and defending the bases, wich is the best use for mind worm units).
One disadvantage the cult has over the gaians is that they cannot switch efficiently to police state and get lots of mind worms supported free, great with the neural amplifier. The gaians, after getting lots of population by population booming in democratics+planned, can switch to police state + green in war time. They can keep a high efficiency while getting a big support rating and lots of mind worms, which the cult cannot. Police state is somehow useless if you can't get lots of research at the same time...
Also, why getting a +1 planet bonus while the gaians get a +1 nutrient in fungus square? The nutrient is much more effective, as the planet reduce so little the eco damage and you can be less afraid to pollute if you harvest the fungus with nutrient bonuses.
Of course they get a brood pit free in every base, but that happens too far in the game and one side usually got the advantage a lot before the cult can get the brood pits. (speaking of multiplayer) I've never played a multiplayer game who got passed 2200, before the brood pits, and I from my exeprience everything happens before that time, the crucial part is over when you get the brood pits, unless the game is really really a close one and stays close all the way along to centauri genetics.
From my opinion, the cult doesn't even have a single advantage, only big disadvantages, except a +1 police effect with the mind worms you capture some at the beginning (and you can't capture a lot compared to the number of bases you'll have if you expand a lot). Even harder to get the projects, a -1 industry(-2 without wealth) might be fatal in multiplayer. Mind worms are not very important strategically, except for defending the bases against attackers and ground units. I take them only if I want to have a disadvantage vs the other players in the game.