I actually really like the idea about questioning players as to why they use the setup or play styles that they use to see if they can provide intelligent strategical reasoning.

Yeah, also inspect their subclasses, and ask if they have their secondary subclass levelled up. Make sure you're knowledgable enough about all subclasses so you can determine wether they're using a decent setup. (Ie. Are you Taking Weapons of light, or Blessing of Light) (Self Revive or Radiant skin) etc. [spoiler]Ive gone through this over 100 times with all sorts of players. I'm very stingy when it comes to people and their skill. Some people are big talkers but can't play, some people are dead quiet and are superb. Also, talk to that person, if they're easily irritable drop them Immediately regardless of their skill it will save you a lot of pain. [/spoiler]

I actually encountered a situation similar to this yesterday while attempting a flawless raid attempt on normal. We were at the conflux section and this level 30 Titan kept throwing up weapons of light bubble. I questioned him on this and suggested he swapped to the blessing of light perk as our only real goal was to stay alive for the flawless trophy, but he insisted on staying on weapons of light because he "liked killing things faster"

Thats actually a rather common issue ive noticed with a lot of Defender titans which is why its a good indicator.