I'll say this one last time.
It's not about Manann sending a storm to destroy your ships. That is a potential thing, but not the main thing. The main thing is the fear of all the faithful on the coasts and rivers of his potential wrath. It's these people, who do your fishing, you do your naval trading, who could come to or leave Ostland by boat, that are the main thing. And their fear of that wrath will, as I have stated previously in a much larger and angrier post than this one, will drive them to run from the waters. Your trade will dry up, because people will be afraid and will not come to Ostland, or set sail from Ostland. Your fishing boats will not sail. Your coastal settlements will wither and die, and it won't matter how many Greatships you try to build, the Cult won't bless them forth from the docks, and the crews won't crew them. Because they are afraid of pissing off Manann. That is what Maghda is trying to get going here. For all affected peoples across Ostland, and further beyond who care, to see and think and say 'Ah, Manann has been appeased, thus we can and should sail our boats and fish our fish and so on and so forth'.
The People. Of. Ostland's. Coasts. And. Rivers. Are. Afraid. Of. Manann. They also worship him, because fearing and respecting him is literally the whole deal of the faith, placating him and very occasionally getting spiffy rewards. Spitting on their faith, stomping on it and saying 'it doesn't matter, shut the fuck up about Manann it doesn't matter his desires don't matter' will quite simply not work.
And I can only take anyone advocating for worship of Stromfels, of whom worship of is forbidden on pain of DEATH across the entire Empire, something that Magnus the Pious and every Elector Count and every other Religion agrees on, as arguing in bad faith. And pirates either worship Stromfels, or Manann. The only secular pirates are dwarfs, and even then they pay heed to Morgrim, and are intensely superstitious. Frederick would have to turn his sword on his own head.
Maghda has strongly suggested not going for the most dangerous of them all - the shark dive being 9/10 fatality rate, has said-without-saying that she's really expecting Frederick to benefit from the healing of either the Light of Summer or Adira's magic healing, and that she's trying to keep the waters safe from any major other dangers in Keelhauling. She had explicitly refused to try and tear out the treasury of Ostland, and instead has offered up an opportunity with things that are far more in line with the actual faith, as in 'sacrificing storied ships to Manann are consistently a well-favored sacrifice' as per canon materials, while knowing that doing so is in fact exceedingly cheaper for Ostland's treasury in the long run rather than the insane fines being demanded by others in the Cult. She has explicitly stated she doesn't want this to get into a fight between the Cult and Ostland, and wants this to be concluded swiftly so that the angrier and most violent elements of the Cult quiet the hell down with Frederick definitely still alive and capable of acting and doing things at the end. She did not yell at Frederick out in the open, in front of everyone, and she deliberately sent her bodyguards away so that no one would see the two of them rather casually and frankly discussing matters, accepting the failures of her predecessor and the Cult while frankly pointing out that every Cult has had problems - and that she's still working hard to solve hers. She has ruled out the other methods of Penance that Frederick quite simply could not do, and has come damn near close to outright saying 'hey, man, let's try to keep you as safe as possible and not dead, huh?' without actually saying it.
It could be because I'm the one writing it, author blindness is a thing. But acting like she's demanding Frederick bend over while she pegs him with a narwhal horn strap-on instead of trying to be as straightforward and swift as possible about this matter so that the faithful of Ostland can be reassured so as to bring no harm to Ostland's economy and people, the mobs of Marienburg placated so they won't bother Frederick anymore, and Frederick able to continue on with his life without having to deal with any of this again, possibly even gain an ally against House Rutger while within Marienburg though she doesn't yet know that Frederick is an enemy of House Rutger, I just...I don't see it. I really don't.