I should have phrased myself better there. When I say "normally nulled", I meant practically useless. Since stacking only on race modifiers will make you lose TONS OF DAMAGE.
Although, I did assume the race modifier was capped because back then when I tested, hydra cards or goldenrings simply do not stack with 2x fbh. But that might not be the case now.
It comes down to the damage calculations. It is just not worth stacking demi human damage when you consider the calculations being used, that and the fact that most classes will only have 4 slots.
I'll give an example. Let us say all cards and effects stack well together. I have a 4 slot weapon and is using 2x fbh shoes and ROP.
Goldenring cards
Let us say I stacked 4 of them in the weapon. The only calculation that will be checked would be for the race modifier damage.
.25 for goldenrings, .10 for the rop and .50 for the FBH
(1+.25+.25+.25+.25+.50+.50+.10) = 3.1 or 310% increase
The normal card combo
Let us say I used 2x TG and 2x Skel worker. Now I have three damage modifiers that can modify my damage.
.20 for tg, .15 for skel worker, .5 for fbh, .10 for ROP
(1+.5+.5+.10) * (1+.2+.2) * (1+.15+.15)
First part is the race modifier, 2nd part is the general, 3rd is the size
(2.1) * (1.4) * (1.3) = 3.82 or 382% more damage.
That's roughly 72% more damage, even if goldenrings give more damage on paper(25%x 4 = 100%) compared to the 2xtg and 2x skel worker(20%x2 + 15% x 2= 70%)
Now these calculations still are not complete(missing elemental modifiers and other things) but at least it shows how much damage you lose by stacking demi-human damage.
Actually, the 10% increase from the ROP is so miniscule if you are already using 2x FBH. You might see some difference, but it might just be a few hundreds or thousands against someone with no ROP. This is also the reason why I consider Emp Auras better than ROP because of the stats.