Some test I made
1. Base Lightning damage of Callidor: 328
2. Let’s add 45% Total Damage from 4p bonus of Vanquisher:
328 x 1.45 = 475.6 <- ok
3. Let’s add to that 170% Total Damage from transmuter:
1282 is displayed. As it turned out 328 * (1+1.7) * (1+0.45) = 1284
The answer is - These two Total Damage Modifiers are multiplicative
If they were additive, we would get 328 * (1 + 1.7 + 0.45) = 1033.2
This is contrary to what I found on Discord in multiple messages.
Maybe it was simply repeated over the years without testing by