You might want to consider the points in this thread:
As for the dual vs single generator, I think Odyssey’s End is better on paper but you need to be very careful with managing the entangling shots. If you mistime it, everything gets untangled and your damage drops by a lot!
That said, I prefer the Fortress Ballista setup but I run Flavor of Time instead of Squirts. I use the shield to provide sustain while I strafe inside oculus rings more easily. I was able to clear a GR130 so far with such a build at 3k paragon.
Update: I attained GR135 so far with Fortress Ballista and just under 3.1k paragon.