Ahh can't remember Sephs actual strength.. speed is Vergil's, as is regeneration and slashability.. real word.
More likely than not Verg would blitz slash Seph into pretty ribbon. Though Seph's materia and other powers aren't to be scoffed at here. DT does give him some more edges to work with..
Vergil 7/10 w/o DT. Better odds with it