Enemy Health Values (Updated for Patch 1.06)

I think the orb weakpoint modifier is based on whether it's pointing at you, or how far away from 90% it is. If he's pointing it straight at you before shooting you get max damage, but when it's pointing perpendicularly you do less damage.

I'm not testing numerical values, but on solo bronze, it seems to take almost twice as many shots with vanquisher if I only fire when it's spinning vs only firing when he's charging a shot to fire at me.

You could do numerical tests on a run where you only shoot while he's charging up vs a run only shooting when the orb is spinning and not pointed directly at you. If my hypothesis holds, every shot should give identical damage while the orb is pointing at you and charging, while when spinning it should be different every shot since you probably won't hit it at the precise position twice in one kill.