Chrom breaths are normal AoE spells, i dont know if you ever leveled characters properly -but i did more than 10 times- and when mobs are using AoE spells, channeled AoE's etc., they dont move from their position when you LoS them or the spell. I think its a global script that all NPCs have. Exception to this would be AoE's mobs use by targetting another player as the center of the spell(such as various flamestrike spells) but we all know that Chrom's breaths are not centered on a player but rather himself, affects the entire area within his LoS.
So, as breath cast takes 1.5 seconds(or so says my bigwigs), any Tank with brain, stable interweb connection and something better than a hamster powered calculator can LoS breath casts and so can the rest of the raid. Only LoS bug that exists in Kronos is that mobs are able to attack behind LoS. Even if that bug didnt exist, I'm %100 sure any competent Tank can LoS the breath right when Cast starts, reposition Chrom after it ends because he will be moving a bit to attack the target with highest threat, and repeat the circle every 31.5 seconds.
So no matter what you say, its a legit strategy. Whatever bullshit some dude speaks doesnt hold any truth.