This boss is very much the same on Heroic outside of two new additions to the fight.
The first is Viscous Horror. The Viscous Horror will rush towards Primordius and explode for heavy AoE damage. This can be feinted so the damage is made minimal.
The second is that Primordius can now stack up to four Evolution which simply grants him a new ability and 5% more damage per stack.
Class trinket helps to trivialize this fight quite significantly
If you have Class trinket, use the Deadly Momentum Glyph and Marked for Death. This will make it to where you can easily throw out ranged Eviscerates to keep constant 5CP duration on Slice and Dice and Recuperate and will of course reduce CD of abilities but more importantly allows us to maximize time spent on using Eviscerate.
I recommend a mouse over macro to maintain auto-attacking on the boss.
The macro I used specifically is:
/castsequence [target=mouseover] Marked for Death, Eviscerate.
One major thing to note is that if a Living Fluid reaches Primordius with the Marked for Death debuff on them the cooldown will not be reset.
Mirror of the Blademaster can also help here as it will keep any Living Fluid from reaching Primordius for a short time (20 seconds). Additionally it will also proc the Deadly Momentum Glyph.
Pulling Primordius to either the entrance gate or the exit gate at the start of the fight serves to simply make the Living Fluid come in at a more desired pace than standing in the center or directly next to a pool.
nevertheless gather 5 mutations and then pop all offensive CDs.
Minimize the amount of Defensive cooldowns used prior to player mutation as Primordius will start to deal significant damage due to Malformed Blood stacks.