2 Blood Strikes will do more damage than 1 scourge strike.
2 Blood Strikes generate the same runic power as 1 scourge strike.
I can scourge strike often enough to make sure my glyph of scourge strike makes my disease last 9 more seconds without the need to refresh them without the use of death runes.
This means that reaping is useless. If Death Runes are useless in pve to Unholy Death Knights, then there is a problem.
Allow Scourge Strike to generate 20 runic power at base value. With dirge this would be 25. If Death Coil becomes too much of a problem, transfer some of it's damage to unholy blight to offset it, to keep the same dps with the buff, but reduce burst in pvp.
This would also make the unholy blight glyph better than crap.