There are obviously other variables that go into the calculation but if you isolate that one would it not be
(assuming that a CD set is being used giving an additional 30% CD)
With a base dmg of 3000 and a CD primary of 42%
3000 + 3000 * 2.22 * .5 = 6330
or
With a base dmg of 3000 and an offense primary of 8.5%
3000 + 3000 * .085 + ((3000 + 3000 * .085) * 1.8 * .5) = 6184.5
So if my math is right the CD triangle would win out by a small margin which would hold with what you see on swgoh.gg with regards to the most used triangle primary for KR.
I can do the math for an offense set but doing math on your phone in a coffee shop sucks.