That occurred to me too, though I suppose one could argue that Jack can create singularities, but she just doesn't, preferring instead to favour her characteristic brute force approach. Could Samara create a singularity? I forget. As for Thane, perhaps a "takedown" ability, similar to that one they later gave Kasumi? Something that bumps up his damage resistance, speed and makes him harder to hit to allow him to get in close and either insta-kill (for cannon fodder goons) or damage and stun-lock (for the more formidable types.) Would have been damn useful to deal with those rocket launcher wilding enemies that just sit there and spam you to death.