That's a loaded question.
The way I see it, power levels is very much an anime thing, to measure someone's power by how hard they can hit is their staple. However, Nero can hit very hard, harder than Dante, but Nero can't beat Dante, so that doesn't help determine what they can each do as though a chart might provide numbers to be stacked against each other. Men has a tendency to label all that he cannot understand in an effort to make the unknown less frighting, and these particular men are demons, creatures of an unknown nature making labels and stats less reliable. Then again, DMC4, unfortunately, went with a style that is rather akin to anime so a lot of this can now apply, so...
Still, been demons a measure of abilities and powers it's not a solid thing that can be quantified in the same way a man's cannot be either. What I mean is, for example, if an office worker whose never played basketball would provably be measured by the standard of never having done it, thus indicating that he would be terrible at it but in truth it won't reflect how well he could do if he does try it; in other words, just because he's never done it it doesn't equate to 'he can't.' Similarly, if Vergil, for example, wanted to teleport to the other side of a wall, or even walk through it, though he's never done it before, it's not in the realm of impossibility for him to pull it off. I know Dante knows when the phone will ring even before it does, I know Nero has tremendous brute strength, and Vergil can summon phantom swords he can use to impale enemies, and while the others haven't demonstrated those attributes it's very possible that they could, specially in the case of Vergil and Dante who are twins and what one can do, it's very possible that the other can, too.
I'm not saying it can't be done, just that there are a lot of unknown variables to consider.
