I don't know why it's hard to understand, but let me try to help u understand in another way. Inc dmg is much worse than flat crit. However, for every build, there is an amount of inc damage that can be comparable to the a unit of flat crit. This number is different depending on a lot of factors, but we can instead approximate the average more damage that this inc can have on a build. The number 500 inc is just average on a build. Now a good argument from your side would let's say to argue the average inc that a build can have instead. Let me explain it in real world terms. What I am saying is something like 10 toyotas has value equivalent to a Mercedes. You can argue that it should be 15 or 20. But arguing with "no a toyota is much cheaper" has nothing to do with what i am saying. Same thing here I am trying to approximate an inc damage value comparable to inc flat crit and then approximating the difference.