We have hunters in our raid so this makes it a lot easier to deal with in phase 3/4.
Our raid comp is 2 melee, 2 tanks, 3 heals and 6 ranged. We let the melee stay on the boss pretty much the entire time from 40% on as obviously sending them to deal with shadows isn't viable. When infernals come in, we have 2 hunters kite two of them and leave one in melee. This one is melee is the only one the melee swap to, unless one of the others is going to hit full energy (which it shouldn't). Every ranged dps swaps to the infernals, and dont hit the boss until they are dealt with. We assign hunters to the shadows as they can basically one shot them in a GCD with instant aimed shot (which will almost always be a crit since its a target with over 80% hp).
We normally get two-three banishes go out from 40% to dead. We send a tank, heals and 3 dps the first two times. We consistently seem to get one star spawn before the add dies, and the second star spawns right as we leave the nether. In our case, we nearly have archi dead by the 3rd banish, so we sacrifice the lowest healer and dps when this happens, so the boss wont heal and the highest dps players remain in the fight.
We spread in a sort of semi circle around the boss, with the hunters standing closest to the living shadows spawn points. Spreading in this way minimises damage taken from demonic feedback and gives people space to deal with wrought chaos without hitting multiple people. To deal with chains, we tend to break two around the same time, let ourselves get to stable hp, then break the last one. Despite all the shit happening in the last 25%, you don't need to move much. On normal the rain of chaos damage isn't that bad, the more you can stand still the better. If you do happen to get caught between a few swirlies, pop a defensive.
A lot of deaths in this part of the fight comes from the overlap between Rain of Chaos and chains. If this does end up happening, the best way to deal with it is stand still. Wait until Rain of Chaos is over before you break the chains. Our guild wiped countless times in the last 25% because they felt overwhelmed by the rain of chaos and prematurely broke chains. A better way to deal with this is to stop dps entirely if you are apporaching 25% and chains are incoming. Deal with chains first, then push him to below 25%.
Also we hero as soon as our first banish team is done, which roughly happens when the boss is about to hit 25%. This is the best opportunity to deal damage to the boss as ranged, so save cooldowns, 2nd pots, hero and the ring for this window.