Currently, the Twilight Matriarch has too much utility to justify choosing the Tormentor morph:
1) The difference in DPS between the Matriarch and Tormentor morphs is marginal (especially considering the Tormentor is only useful for targets above 50% health).
2) The burst heal from the Matriarch is one of the best in the game as it affects 2 targets, with a 360 degree hitbox, and can crit as high as 20k+ on non-healer builds.
The Matriarch was intended to be the 'healing' morph whereas the Tormentor was designed to be the 'damage' morph, but currently the Matriarch functions as the 'high-damage-while-also-providing-high-survivability' morph. There is hardly a justification for using the Tormentor morph when the benefits to the Matriarch outweigh the ever so slight increase in DPS that the Tormentor provides.
A skill which functioned similarly, but received a rework, is the Path of Darkness skill and its morphs from the Nightblade toolkit. Previously, one of the things that made Magblades outperform was the fact that one of their skills provided both high damage as well as healing (not only for themselves, but for their group). The skill has now been reworked so that Magblades have to choose between a morph that will either 1) Provide damage or 2) Provide healing. Not both.
I suggest that the Matriarch receives a rework so that it does not deal any damage at all, but that it functions similarly to the Cauterize skill from the Dragonknight toolkit. While summoned, the Matriarch would heal a single ally rather than attacking an enemy and the active burst heal would remain unchanged. This would strengthen the Matriarch's position as the 'healing' morph and provide better balance between the two morphs.
I say this while my main DPS character is a Petsorc. I have a horse in this race, and even I realize that my horse is outperforming. I shouldn't be able to reach 50k+ dps while also having access to one of the best burst heals in the game. Reworking the Matriarch so that it provides more healing at the expense of dealing damage would put it in line with other similar skills from other classes (Path of Darkness, Inferno, etc.) while not nerfing it to the point that nobody would use it. The Matriarch would still be attractive, if not even more attractive, to Sorcerer healers and it would give Petsorc DPS more incentive to actually use the Tormentor morph.