Do you seriously think a 30 man raid can just ignore infernals? EVERYONE have to swap to them. There is no excuse that you can keep hitting the boss cause then you will wipe. Only cause you have a beam on you doesn't mean you can't dps.
Shackles I can buy that it is a bit more important to break them a tiny bit earlier as it's a ticking dot ramping up.
What movement??? Move 3 yards so the beam doesn't hit people? Move out 10-20 yards to pick up infernal if you are a meele? That is meele only. Ranged barely have to move to reach them when they spawn.
The tuning of damage/healing around raid cds are the main problem on this boss fight. Not really the mechanics themself.