there are plenty of fights that ranged have a much easier time on than melee. in regards to twilight ascendant council, on the beta pretty much all of our melee would be dead 10-15s in to p3 when we tried hardmode. as a raid leader I would do exactly what paragon chose to do in that situation.
off the top of my head, other "anti-melee" fights include:
halfus, especially hardmode. on HM you have to stack drakes up to cleave them down, meaning you get like 29 giant wings flapping everywhere obstructing your view and making it extremely hard to dodge the fireballs, If you take a fireball right before the flame breathe you will probably die.
Omnotron, not really that bad but if your melee aren't paying attention they can get gibbed very easily by spawning toxitron adds.
Magmaw, melee can't viably help with killing parasites (or constricts on hardmode) bringing just enough melee so you can chain the boss down is most efficient
Atramedes, melee have to react much faster to the sound balls that spawn under the boss than the ranged do, melee can't DPS the boss during the air phases.
Valiona, guaranteed to splash the shadow bolts, requiring extra healer mana to be used.
Cho'gal, after a few adherents melee are more or less guaranteed to be fixated by at least 1 blood of the old god, meaning that they can't help kill the bloods. also if your raids DPS blows they get raped by the fester blood, ranged don't have to worry about it unless they are being dumb. ranged in general have to move much less on this fight meaning they can be much more efficient with their DPS.
conclave of winds: melee have to run away from the adds when they start doing their purple detonation thing, ranged can keep DPSing.
Nefarian, melee DPS in p3 can be limited by fire placements, also in p2 you can't help DPS nefarian.