If you want your vanquisher in the abyss, equip it while your forming the bridge into the hellmouth. I don't know how your game works, but if I finished the nexus and went strait to the abyss, id have plenty of time to change weapons IN ORBIT!!! NOW let me help you with a valid argument. Devils Lair nightfall with arc burn. Your running with fatebringer, patience and time, and song if ir yut. But for that brief time the solar shielded wizards or Thrall are out, you want your VoC. That would be a legit time for a quick swap, although one person in your fireteam agreeing to carry a solar weapon negates the need.