There are many problems with the LB. One of them is that in many (not all) cases, by the time LB2 is built up for a melee, the boss is commonly either dead already or at 2% or so. I feel that there are plenty of times when a melee is in the middle of their "big DPS" rotation where it makes more sense to complete that than it does to hit the LB button. Sometimes, that's why they sit on the LB until 1%. There are also plenty of times where the LB is just forgotten about because frankly, it isn't that big of a deal to use it... or not use it.

I find the LB has had more use as a trial/raid tool where you have to save it for some big boss mechanic that will wipe you otherwise. Then the tanks are always Johnny-on-the-Spot with it since it is the only time the LB actually matters. But even then, it is a "if you don't use this, you die" situation. So, it isn't like there is a choice in the matter.

Personally, I find that LB1 by ranged/magic on trash can be better. However, that only seems to hold true when NOT doing level 90 content. Trash in expert roulette just melts anyway. But, if doing level roulette where everyone is level sync'd and don't have their full DPS kits, burning some trash with ranged/magic LB1 tends to be worthwhile.