A few of my thoughts on the subject.
1) The Psukhe is a sorcerous practice based on passion, not intellect. It is invisible precisely because of that. Even the the more intellectual practices of sorcery has limited understanding of their own metaphysics. The Cishaurim are going to under even less because blind faith is what makes them good sorcerers.
2) Since even the metaphysical understanding of Anagogic Sorcerers and Gnostic Schoolmen of their own practices is limited the same follows for the Cishaurim. The do not have the Mandate's knowledge of the Consult and the Tekne. The Scarlet Spires are known to be arrogant practitioners of unholy arts, they are from the Cishaurim's point of view, natural suspects.
3) That said the suicide strike, while not inconceivable for fanatic priest-magicians, is something we do tend to expect from those under the influence of the Dunyain.
4) Moenghus's lack of command of the water is absolutely relevant to his ability to influence the Cishaurim. Kelhous didn't declare himself a prophet, he displayed overwhelming wisdom and insight and his followers came to believe he was a prophet. Moenghus's weakness is going to undermine him just as failure would have undermined Kelhous. He's still a Dunyain with the ability to manipulate people but his ability to read them by his blinding and his authority is undermined by his weakness.