Split your raid in two equally-size groups, one on each side of the boss. You can use the metal grid on the floor to align the groups. Every time Argaloth casts Meteor Slash, you want the tanks to switch. Half of your raid being stacked will help minimize the damage, and the tank rotation will make sure that nobody eats a second Meteor Slash while the increased Fire damage taken debuff is still on. Consuming Darkness is a fairly nasty DoT that should be removed as quickly as possible.
At 66% and 33% Argaloth will start channeling Fel Firestorm. Simply run around (individually, not as a group) without stopping for the duration of the spell, making sure you are back near your assigned position when it's over.