I imagine TDE is weaker than Mundus, but only slightly. As I said before, Mundus had to dethrone Argosax to become the ruler of Hell. Or maybe TDE actually is stronger than Mundus, and that's why Mundus didn't kill Argosax, because he knew TDE would be released. Either way, DMC2 Dante is on a ridiculous level of power.
I think the really impressive thing is that DMC2 Dante managed to kill both Argosax and TDE without a devil arm, whereas Sparda sealed Argosax whilst he had access to his own sword, Yamato and who knows what other devil arms.
Random thought - is Rebellion actually a devil arm? The DMC wiki classifies it as one, but it doesn't really seem to have any extra abilities that the others do. The only things it's done that makes it seem special is the crossguard, hilt and pommel changing when Vergil stabbed Dante with it. All the other devil arms have either an elemental power or some sort of special ability; from Alastor's lightning, A&R's fire/wind, Yamato and Sparda being able to open/close Hell gates etc.