I said "IF". I haven't spent a long time playing DMC2, so forgive me for not being fully familiar with the mechanics. Even still, she can only move 10x faster in DT correct? In which case Nero can possibly defeat her by going DT before her and attempting to AP stomp.
Well, DT are thought based, so it will be probably the answer for each other mid battle, it's basically instantaneous
And yes, every Heart depends on DT
And the DT is still a second being that can attack and defend. Assuming it is around Nero's level, and that it can move on its own, that's two Neros that Lucia needs to react to and defend against. Even if they are 10x slower, they can cover double the angles for defense. This is, also, assuming that she doesn't use any of the other movement hearts in this battle, like the Aerial Heart, and fully leans onto the quick heart.
Now I got it, it heeeeelps against the Quick Heart, no doubt about that, but still, it's a big gap and she will be faster than both, I'm not saying that he will die because of this, but can he avoid one single hit ? The Quick Heart is not the only problem here, you forgot what I said about the Chrono Heart and this:
Even in a normal fight, a clash between swords would happen because that's how DMC characters fight, Nero will only avoid close combat if he knows the effects of the Chrono Heart, which he doesn't
Basically it is impossible for Nero to avoid ANY contact with Lucia if he doesn't know Lucia's Time Hax
I don't think you believe that Quick Heart + Chrono Heart is not a dangerous combo for Nero.