Nope. My claim is "Loghain rewarding and trusting Howe after Howe's treason to his overlord is evidence that Howe did not take Loghain entirely by surprise with his move". That's one of the ways in which you are misusing post hoc. You're conflating "Is evidence" with "is proof positive".
And what you're doing is misrepresenting the fallacy as evidence. What you consider to be evidence
is the fallacy. It's simply a false conclusion.
Deserting your commander on the field of battle and fleeing without any engagement or a "so long sucker" note, would be a difficult case to defend at a court martial.
There was a plan of battle, and Loghain engaging in the plan would have resulted in the loss of Ferelden's entire army, instead of just some of it. His retreat was not abandonment.
When things happen together without causal link that is called a "coincidence". The fact that coincidences happen is what makes post hoc a fallacy. So yes, when you claim the post hoc fallacy you are raising the possibility that these things happened by coincidence, that Howe happened to do something other than slaughtering the Couslands that Loghain liked so much that he ignored Howe being a mass murdering traitor and made Howe his new Best Friend Forever.
Again, no one is claiming that there isn't a causal link, it's just not what you're claiming it to be. The causal link is that he needs support from the nobility, and Howe is literally the only noble he can turn to. And if you ever got the impression that Howe and Loghain were "BFFs" well, then I don't know what game you were playing.
Howe had free access to his private chambers. He followed Howe's advice on multiple occasions. He gave Howe lordship over not just one but two of the nation's most major fiefdoms. He put Howe in charge of the capital.
Yes, he did. Still not evidence that he was involved in the Cousland massacre.
Howe was not Ferelden's other most powerful noble. He was no more than midrange before Loghain decided to give him the aforementioned showers of wealth and honors. Even if he decided to buy Howe's support by affirming his right to the Cousland estate, he didn't have to also give him the vacant arldom of Denerim. He could have easily used that to buy another man's loyalty, one who didn't just murder his previous overlord. Loghain isn't holding his nose and dealing with the mass murderer at arms length. He likes Howe. He trusts Howe, more than he trusts Anora. He lets Howe take custody of valuable hostages, he trusts the finances of the biggest city in Ferelden to him, he gives Howe access to his private chambers, when Howe says "let's do deals with the assassins, the slavers and the goat molesters" Loghain nods. I expect he thinks Howe's a patriot. A man who can be relied upon to do the unfortunately necessary dirty work. LIke killing Bryce Cousland.
You're inferring a lot (again) from absolutely zero in-game evidence. There is nothing to indicate that Loghain likes anyone, much less Howe. He probably likes Anora, but that's it. I certainly don't get the impression that he trusts Howe. What I do get is the sense that Howe is a means to an end. And yes, Howe actually is the other most powerful noble. He doesn't have to wait for someone to grant him Highever, he can claim with Bryce's death and no heirs. Howe is the Teryn of Highever and he achieved it by force. It's sneaky and yes, it's murder, but maybe Bryce should have been watching his back. And again, you have more conclusions that have no evidence. I hope you're never on a jury.