Iaian>DSK should be common sense. But Redditors don't have common sense so no surprise there.
I think it's honestly less doubt of Iaian and more that even to this day people have and still SUPER overrate DSK. Like people think he was some kinda high tier Demon or even bordering on Dragon when in reality he was nothing special at all. Dry DSK had moderate difficulty beating PPP who is actual fodder by S-Class standards at the time. And while he surprised Sonic with his speed, Sonic legit perception blitzed him even in wet form. Then Genos comes along and is literally BEATING DSK. He actually thrashes him initially and still stalemates him with one arm. Genos at the time was still only able to tangle with some average level Demon's, like, well, DSK.
Iaian is outright stated to be S-Class level, put up a fight against Dragon level's in the MA arc, has reacted to Dragon levels consistently (someone actually said he'd be blitzed by DSK btw, wild), and he's able to deal considerable damage to Demon level Monster's. I don't think it'd be easy for him by ANY means but I could totally see him taking out DSK.