Personally I would just ask them, but I'm old fashioned like that. A lot of people level up solo or by playing very suboptimally because the game isn't very hard and even playing terribly works fine for 99% of dungeon situations. They might genuinely not know, or have forgotten about the useless AoE abilities they shoved on a secondary hotbar months ago. Or be traumatised by terrible tanks who lose AoE hate the moment someone throws out a Fire2.

If they're jerks about it, kick away.

The LB thing is annoying but not noticing it seems to be a weird debuff that affects the most appropriate LB user from time to time. I play in a group of friends and the same people always manage the LB yet I'm forever reminding them about it (and occasionally passive aggressively using it as healer just to demonstrate its existence) because of this strange selective blindness