Its really easy to test which does the highest DPS, time your muir runs, one with arcane gate+void star and one with void star spam only.
Unfortunately its poorly designed so its very random. Bosses can easily hit you while you are in the casting animation or right as you popout to attack, and short of having clairvoyance, you cant do anything about it as its very luck dependant. Bosses can also decide to fly away, teleport or otherwise become invulnerable right as you use it.