Is limit break not a thing?

[Vrankyl]

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

If anything a higher HP pool would render the caster and ranged LBs ineffective since they do less ST damage than the melee one. In fact Melee LB is the preferred LB for all content unless a Tank LB is required, or in case of the second boss of Raba the caster one to deal with adds.