Yes there is broken combos. Imo stacking 8 SMNs together and all pulling LB at the same time (200k wide AoE potency) is even easier, but I guess it cannot be done with a light party premade alone. Still, why aren't people doing it? I suspect that most people just want to play their jobs and have fun or do their daily and not bother doing something they don't want to do. But yeah, people could retaliate with a lot of nasty stuff.

My only advice is to just turn off all effects to limited only and you'll see all the DRG LBs pretty effectively from miles away, especially in FLs where everything is so open. Perhaps sometimes you'll insta Guard by reacting to a DRG LB that's actually yours, but better safe than sorry. Also, wasting cooldowns in FLs is nothing on the scale of things. It's back under 30s, this is not Crystalline Conflict where it lasts for an eternity. There is a crapload of downtime in FLs.

My new thing in FLs is to just go for the anti BH5 jobs like WAR, MNK, etc. You literally have all the tools you need to stun the DRG just after their LB, and punt them right in the middle of your team so they get insta deleted. Works against most jobs, and if it doesn't, it spooks them enough that they become less of a problem when trying to pull off their crap.