I acquired spider man 2099 and discovered this syn

Being a r3 venom owner I was very interested to try this. So winter soldier here I come.
Base for my syn team and mastery combo 5 hits. The screen shot is the 5th hit that was critical. I have 2 furies, 3 cruelty and 1 armour up. Respectable 5617 damage

Now time to parry heavy to get the 50% aptitude 2 furies, 2 cruelty (one was eaten for the heavy) but now 1 precision.
My thoughts is with 50% more of what buffs I got should be 1 more fury, 1 more cruelty (but that equals original before heavy) and half a precision but imagine my surprise to see the end of combo come out at 5575

That's right, I actually deal less damage now.
I'm not seeing why this syn should lower the damage at all.