Oh gosh yes Meursault arc was an absolute mess. His presence there raised the stakes but fail to deliver, thus was very sloppily done. I was always of the opinion that arc was meant to be a bit different but that Asagiri changed things on the last notice because of s5

As for Fyodor being deceived, that was always bs to me, for two reasons:

1) who controls the vampires? Fukuchi. Who sent Fyodor to Meursault because he can't trust him? Also Fukuchi. Why would he send a vampire Chuuya to break Fyodor out then? Okay, protection from Dazai, but vampire guards are enough for that. Therefore Chuuya's mere presence there should've already raised the red flag in Fyodor's head

2) Fyodor sent Chuuya to supposedly shoot Dazai, knowing very well all Dazai needs to do is touch him and nullify Bram's ability. Gamble is too high, if he wanted to kill Dazai he could have shoot him himself. Fyodor didn't start scheming yesterday, this is a man who remembered all scratches on a card deck in 5 minutes. Him taking chances with Dazai's fate is just too far fetched. In the best case scenario he could have just left Dazai like that. But no, he sent Chuuya there - but not to kill Dazai but to get rid of Chuuya in a way that doesn't raise suspicion. Fyodor's plan was to die in a helicopter ride at the hand of a vampire. For that he needed to be alone and Dazai grasping nature of his ability (albeit too late) is the only setback Fyodor received in the entire game. Not to mention that Dazai surving the elevator crash was suspicious af. Fyodor not questioning what audience clearly did meant he had a pretty good clue what's going on

Later on Fyodor acted surprised - and he was genuinely surprised. But not by Dazai being alive and Chuuya not a vampire but because he didn't expect to be impaled and caught in that exact moment. He wanted to leave Meursault and explode somewhere in the air, that's why he was rushing Nikolai so much