I have to a point, I stopped paying attention around halfway of Ninja Gaiden Two, and it is fair. Ryu would be a fair opponent, but Dante can basically match anything Ryu's arsenal have or flat out tank it. Dante is already used to fighting a swordsman who can not only deflect bullets with his sword, but catch them and throw them back with the flat of his blade. It's nothing particularly new for him to face.
Dante can match Ryu on the level with speed, swordplay and arsenal fairly easily, and probably can best his swordplay if he really wanted to, or even his speed if he bothered to use certain styles. And that's not the extra abilities he knows and can use with his various weapons he obtains from the souls of demons.
Dante's back up doesn't exist, because Dante rolls solo and anyone else who shows up is just kinda going after their own thing. But even with that insane damage... it won't really keep up to Dante's regeneration, and the absurd amount of punishment he can take. The thing here is that Ryu is still basically easily killable despite his supernatural form he gained.
Even Ryu's OLUTs and Ninpo couldn't really down Dante, who could either nullify them outright, or stop time and just stab Ryu as he is casting. Or, in case he cannot stop it, for whatever reason, he probably could have easily fully charged his Royal Guard in the fight, and go into Dreadnaught, where he is invincible.
Ryu poses a serious danger, but, Dante has all of the answers, as well as a wink and a smile.