Hmm. On Z&T our ranged DPS are in turret mode so single-target is more important. Same with the tanks, though I could see trying to keep dots up on both as a sorc (though that's a lot of movement to stay in position for adds phase). The minefield is a bit of a wash for DPS in general, though the most important DPS is the 'splodin droids so still helpful to have superior single target DPS. On the last boss there are opportunities for AoE (first add phase) but the two droids, bomb mobs, and the last boss are single-target DPS.
I have no experience with sniper DPS, so I have no clue how much better they are than mercs so I'll have to take your word that they are superior as ranged DPS in operations (though the severe lack of movement is concerning...).
To be clear I see your signature and my guild has not cleared EC HM16 (we only raid 8M and haven't cleared EC HM, only story mode), so the disadvantages of turret single-target DPS may become apparent soon.