We know Katarina's father had to be pretty strong as he apparently spanked 
without too much difficulty and logic should dictate he is stronger than 
being that he outranks her and he taught her everything she knows. So would this make him the 2nd strongest in noxus behind 
or 3rd strongest behind 
. Being that both Darius and Couteau have the same rank they both should be around the same level of strength?
He might be at an equal level as Darius, or, you know, there could be more depth to it. Like say, each have varying strengths in different styles of combat and diplomacy. I'd imagine that Couteau has a keener mind for tactics than Darius, but, of course, not as keen as Swains.
General Du Couteau was implied to be OP as fuck in regards to skill, power and influence in Noxus. He seems like someone that would give anyone that messed with him a hard time and his disappearance may because he was loyal to Darkwill, he discovered that the black rose is up to something nefarious or he was just when missing by accident and Swain didn't need him back yet. Unless Riot reveals what the fuck happened all we can do is speculate.
I think that he was the most likely to become the Grand General of Noxus after Darkwill until he dissapeared... So, i guess that he is/was the strongest/most powerfull person in Noxus.
If I remember from 
's old League Judgement, that time when Du Couteau had to leave, presumably either to meet the other Black Rose members, or fleeing them, he was scared. So he's strong...but not so OP that he wasn't scared of a bunch of assassin's aiming to kill him or capture him.
Him versus would be an interesting fight, though I'm still not sure how short-reach daggers fares against a guy with a giant axe and heavy plate armor. I mean, medieval fighting rules, Du Couteau doesn't really stand a chance, but uh, he taught 'magic' to Katarina and Talon somehow what with their blinking here and there, so maybe Du Couteau can Naruto that fight.
Against ? I don't know how to quantify dagger guy versus giant demon bird guy honestly.
There was that Dominion CGI trailer (which was never officially released but is still around on YouTube), where 
(real one) and Swain are fighting. Here's the bit of Jarvan vs Swain in the Dominion cinematic trailer:
https://youtu.be/5LMQBxx28zo?t=2m41s
It's a rare thing to see them actually brawling, but interestingly, looks like even physically Jarvan was actually losing to Swain. Swain, in raven form, dodges his attack and knocks him to ground in one swipe. Then Jarvan stabs him but Swain shrugs it off, and starts sapping his life before Jarvan Ws in retreat.
So yeah, I think if Du Couteau's main ability is physical stabbing, that probably wouldn't work on Swain, if Swain is already in demon bird form because he'll just heal it right back up, and even though it's not reflected in in-game stats, it seems like Swain does get physically stronger in bird form. Maybe if he surprises Swain before he gets a chance to transform.
