Overall, I agree with your assessment of Darkglare’s functionality and primarily favoring one build or another. The fact that it is not all purpose and useful to every build makes it much less useful as a general purpose damage cooldown, this is why DSM would have been a better cooldown (if perhaps boring on paper).
Now, an aspect about Darkglare that I really do like it the dot extension, but it needs to work with that new pandemic refresh trait. If it counts as refreshing the dots during that window on multiple targets with ways of spreading more copies of our other dots onto targets (maybe by modifying Nightfall or Drain soul to spread dots) then we would have a way to interact with it in a way that doesn’t just favor one build. The dot extension element does feel a bit too much like the HoT extensions of other classes in many ways though, and as such is not as interesting as it could be. I am honestly surprised they have not put more aiming and timing effects into the game, as they have to a of vehicles in the past couple expansions that have had such gameplay elements that felt really interesting and fun. It would be awesome to have angled skill shots that required some positioning and timing to land but extended dots. In fact, that could just be how Shadow Bolt worked in general, a skill shot that extended dots for Affliction, and a targeted shard builder for Demo. I see no reason they have to function exactly the same way for each spec but only provide a bonus for the other spec.
Only reason the game is stagnant and boring right now is from a lack of innovation. They have shuffled systems and priorities a great deal, made numerous changes to things that may have broken some things, and really have their work cut out for them to actually turn things around now. If they want the game to really succeed they will need to adjust their focus toward specialization tuning behind just gear and numbers. The focus really needs to be tuned in on the mechanical play of each spec and class now more than ever, due to the design of the classes being so sparse.