Maybe you should read MaRin's quotes again. And again, win rates suggest otherwise. It's a pretty even matchup with Fiora scaling better in the late game.
Again, MaRin did a lot of dumb dives, and even still he was consistently driving Darius back.
In regards to his ult, with 40% CDR it's on like a 40s cooldown. He can keep using it to drive Darius out of lane as much as he wants.
I dunno dude, you're just showing a fundamental lack of understanding in terms of how the matchup works.
So what did Marin say? Did he say he picked into Darius? Nope.
He explains when Fiora has items, Fiora is stronger, but didn't say for what. Obviously, it's for split pushing, while Darius will absolutely monster Fiora in lane.
Diving towers? I guess maybe you didn't see Darius killing Fiora under her tower. You made no sense
Darius will Q, maybe Fiora will get Riposte off, but then it's followed up by Apprehend and Crippling Strike. It's a completely uneven trade that Marin, in those very games, use Grand Challenge and Flash out in order for it to be even. And even if it ends up even, Apprehend sets Marin up for easy ganking. Not having a 40s cooldown for a TP flank is game changing and could have tipped the scale on many lanes elsewhere.
I don't know what you were watching, but I was watching Darius dominating laning phase against Fiora that even the casters were questioning Marin's abilities.