I think that can be called overcompensation. For a +6 ability to be able to kill even atropals automatically with a 65% success rate is a tad much.
Actually, uh . . . I need to change my stance here . . . I read up on the undead in both books and checked the abilities themselves (+2 and +6 respectively), and decided that both are perfectly fine as-is.
You see, undead have crappy Fortitude saves. Even Nightcrawlers have only a +8, and Disruption is a +2 ability. Greater Disruption is a +6 ability. The best undead has a +22 save and is CR 50, and I think that something designed to challenge Level 50 characters damn well should be able to survive such abilities.
So in conclusion, I see nothing unbalanced with both abilities as-is. Both have reasonable saves and conditions, so . . .
Perhaps you should make a +10 version called Ultimate Disruption that is DC 33?