All things equal, a DRG should beat out a NIN in a straight dps race by ~5-10% or so. If he's rocking significantly better gear, it'll be easy for him to edge you out. If he's got a WAR supporting him so he doesn't have to Dancing Edge, he'll close that gap. In those solo parses, though, there's no party buff or party support, just you on the dummy.

It's also possible that you had an unlucky run and he got a really lucky one. I killed the A5S dummy at i210 with ~2-3 seconds to spare, so it's also possible you're missing something significant or just not doing the rotation properly at one point or another.