Though I agree that the super death mega spells were a heavy handed response to the rudimentary death stars the design team undoubtedly used in play testing, I believe they were undermined by the 7th ed books still in use. consider that in our meta there are two 6th ed books and two 8th ed books (so no ridiculous death star combo's). simply this has forced my dwarfs and my friends wood elves into MSU as big units of Dawi die to a huge variety of things and the only spell i now fear is pit of shades (as it removes my 350pts lord choice without me rolling any dice). the GW designers (yet again ) have failed to take into account the ingenuity of the community in getting around threats! I put it to you that it is units that get around these spells that are the real problem as they force you to think of a unit to deal with them and in so doing making you vulnerable to the spells that are meant to prevent such units.
the real failing of the spells themselves is in there blanket effects, if they had built in modifiers for monsters (say +2I?) or if they only inflicted one wound.