

Okay first things first. I want to start by saying that I don't think Nero is superior to DMC3 Dante or anything but I do think he has a chance of doing this by himself. Now while Dante did require Vergil's assistance to finish off Blob form Arkham, I believe it was more or less because of Arkham's crazy amount of endurance. I don't feel like going into too much detail at this time so I'll just say after some research and scaling his power increase from the manga to now, DMC3 Dante's strength at base form is large building+ Basically that means if he were to use a full powered Stinger at something like a Panera's (for example at this size)

That suckers going down no questions asked.
I'd also rank Dante at being massively hypersonic in both speed and reaction timing. Vergil can very casually time bullets to the point that he doesn't need to dodge them. Instead he deflects them and even sends them flying back at Dante, maintaining the same speed (if not more) that they had when they were sent towards him. He did this with several fired shots might I add. The truth of the matter is, bullets are apparently much to slow to give Vergil any trouble. Dante had fought Vergil to a stand-still on many occasions and even blitz him during their final enounter.
His trickster style really amps (or rather focuses) his speed at well.
...Back on topic, the point is I feel that if Dante had a bit more destructive power, he could have probably soloed Arkham. To support my evidence is that fact that Arkham was using Sparda's power to boost himself, giving him way more power than he would have otherwise, this include strength and even heavier endurance. Look back at DMC1 when Dante turns into Sparda's DT. Not only does her traverse through space but he has the endurance to tank meteorites and land back on earth and into Mundus' realm without any real issues.