Spell-Like Abilities (Sp) or Psionics (Sp)
If the base creature has spell-like abilities, it gains +15 to its caster level to use those abilities. A paragon creature also gains the ability to use greater dispel magic, haste, and see invisibility three times per day, even if it did not have spell-like abilities before, at 15th caster level.
So, warlock legendary monster has CL 27. I rule that if warlock gets ways increase their CL it applies to EB also (so if want go arcane blaster then warlock is the prime choice). The other casters have choices to do other stuff with their spells (like pick orb spells, buff spells etc). Or we can rule that above feature also applies to legendary monster's CL with any class with CL (so yeah, Wiz 3/Cleric 3/Mystic Theurge 6 has CL 24 with arcane&divine spells but knows only 5th level of them).