We have here a Hax Gap, actually, a big one
Also, a gap of 2X in AP is not that great, for a one-shot, in VS Threads, you need to be 7,5x stronger in AP than your opponent, that's our rule (at least it was, idk)
Anyway, I'm going with Dante here
The AP gap is less than 2X since he literally stomps Cerberus, who did their 8-B feat by breathing, and he can amp his stats with DT, plus what I said above
For the fight, Dante's Royalguard can redirect even Spatial Attacks that bypasses durability and can one shot another 8-Bs (From Vergil, just like when he killed Beowulf) so Wind Manipulation is not going to break the defense, also, Dante can use this to heal himself with Ultimate Royalguard.
For speed, their are equalized but Dante's Time Manipulation will give him the edge, since Quicksilver is a near stop going by the actual cutscene, and even in gameplay still a great factor. He can also use Doppelganger to double his range and firepower, and Teleportation to help him dodge most of Ouma's attacks
Not to mention Regenerationn, Flight (in case he needs to keep a distance) and Homing Attacks, that are going to hit Ouma in case Dante uses this with Quicksilver, since Ouma is going to be slower than Dante's attacks
Voting Dante