The added leeway is probably there to make up for latency, positioning of characters on the client side versus the server, and the animation lock. I've been the victim enough to know that there are very rare circumstances where I can avoid the damage completely; like if someone casts the LB the instant I hit Attunement, receive a shield, or either I get pushed back by some other ability, or the melee character is stunned.

I still think this is balanced and working fine, since melee jobs generally have range as their largest issue, and having something that still goes off and doesn't waste their adrenaline if it misses or you dodge out of the way makes up for that shortcoming. In other words, this is working as intended. Ranged LB have a beam or large area of effect, to make up for the lower damage and distance. Melee LB is, well: