I don't know if it's been said already but I think as an alternative to having to target another player, cast the LB and then maybe target an enemy or location on the ground, you could just be able to cast LB while someone else is already doing so. Then your character could add to the animation/effect and it would never catch anyone by surprise or whatever.
There's already an animation for anyone who's not doing anything but this would lock you in to their cast timer too.
Example: BLM LB with a Bard helping would add arrows that rain down vs DRG LB with a Bard helping where the Bard would cast a shining arrow at the target. Something like that.