I parse slightly behind SAMs and DRKs, like within 5k damage. The other night was in a pt with a DRK and a SAM, we had BRD and COR buffs, in the main room DD party, not roaming. I parsed 34% SAM parsed 36% DRK parsed 30%. DRK had the delve scythe, not sure if that's good or bad, and he wasn't rocking Souleater either which would have affected his damage I suppose. Anyway, DRG is still fairly competitive. I usually parse all my delve runs and have never been ultimately crushed by another DD. Sure I've never parsed first except on Moth and Raptor but for the most part I'm usually in the top 3 or 4 and always behind by maybe 5-10k damage(out of 300,000+ damage), so 2-3% at most.
Also the extra damage that every melee does when Angon is in effect is more than enough to justify the DRG's spot. So if a DRG parses within 5% of other heavy DDs but when he uses Angon, everyone else's DPS goes up by 10-15%, that extra damage combined is more damage than say a DRK would do if he were in that spot instead of the DRG.
Picture a delve run, 45min, no angon used
Damage(for simplicity, I picked easier numbers)
DRG:100k
SAM:115k
DRK:130k
then with the same run except angon is used, all conditions are kept the same for this hypothetical, only variable is this has angon being used
DRG:115k
SAM:130k
DRK:145k
That 100k the DRG does plus the +45k extra damage thats dealt due to angon means the DRG produced 145k damage which is more than an Angonless SAM or DRK dealt. Of course this scenario has flaws like how fast are melees engaging, which buffs are on, what's the pdif, gear, merits etc. But what I'm trying to get at is, aside from doing respectable damage we up everyone's damage by such a high enough degree that the extra damage everyone else does(in the alliance, not just the party) is significant.
Remember Angon is a -25% defense down which is equivalent to a 33% attack boost--FOR THE ALLIANCE. So not only can the DRG deal tremendous damage and maybe fall short 5-10% behind another melee, he ups everyone's damage by more than that 5-10% he's behind by. It's similar to why DNC can be so powerful. In DNC's case, I think Sylow said that Haste Samba can increase everyone in the party's DPS high enough that the combined DPS increase to each melee from Haste Samba PLUS the damage the DNC itself does is more than what an extremely well geared WAR could produce.