Interesting idea. Certainly the problem with a traditional Death&Despair combo (just the death marks and the veiltek) is that if you come down outside rapid fire range the unit gets decimated by enemy shooting or assault before it can do what it is supposed to do. So, Phaeron would be helpful there. Problem is, if you come down outside of rapid fire, the velitek abyssal staff doesn't go off either, which to me greatly reduces the effectiveness of the unit.
For me the purpose of the unit is to drop in, put wounds on a suitably juicy target (
MC,
HQ, long fangs, termies etc) then die. In the games I have had, that is generally what happens - the unit has one shooting turn to make its points back, then gone. However, happy to do that because the unit is only 160pts and I'm generally targeting 200pts+. It is also a good distraction if by some miracle they do survive (more on that later).
If you try and increase the survivability of the unit (after all 2+ wounds on 2 targets is not to be sneezed at) by adding some
CC ability (which I think is what the lord/Olord is supposed to be doing) then you increase the cost - for 385pts you can get 5 Lychguard (S5T5A2) with swords + boards + veiltek +OrbLord with Scythe,
MSS,
SW instead. That is a
CC unit

. Also, if you use the lychguard, the Overlord can go into the
CCB, which is where he really shines.
If I was going to do the deathstar I'd focus on coming down within 12 inches so you can get rapid fire and use the veiltek. So, I'd be looking to beef the
CC survivability. I can think of 2 ways:
5xDeathmark, Veiltek, Lord with Orb,
MSS, Scythe,
SW (maybe
PS if you have the points) for 235 points. This would free the overlord to the
CCB
Or, if you really wanted to just play with these units behind lines,
(475)
Overlord, Phaeron, Orb,
Sw,
MSS, Scythe,
PS
Veiltek+Shroud
Stormtek + Lightning
Deathmarks x 5.
As all members of the squad wound marked units on 2+ (remember this is any marked unit) this should effectively deter your marked unit from assaulting you. You also have the shroud if you are out of abyssal staff range, lightning to further deter specialist assault squads, and Haywire to make a mess of nearby vehicles. Course, this is pretty expensive.
If you just wanted to tweak your original idea, I'd do this
Overlord, Phaeron,
MSS, Scythe,
SW
Veiltek
lord, Orb, scythe,
MSS
5x Deathmarks (395)
I reckon this gives you more flexibility (you can detach the Overlord after you land and he can go off and crack some vehicles) and better
CC deterrent. Whenever you get a lord with a war scythe, get
MSS. It is SO worth it.
BTW, watch out if you start on the board because you can only mark units on the battlefield. I don't think you can mark units in reserve.