Is limit break not a thing?

[Bourne_Endeavor]

-may not be useful at all (shinryu in particular, he has so much hp melee LB is less effective)

...

Let me get this straight. You think a 9,000 potency attack is less effective on a boss with... more HP? Unless there are adds, melee LB is always superior.

Anywho, a big reason you won't see it in harder content is people care more about their personal numbers. LB has a long animation delay, thus melee tend to hope someone else will do it.