So, will critical damage mod sets now be useless?

Thanks for the explanation/clarification Woodroward. You are correct, the formula I was using was definitely simplifying things because of how offense from the mods applies. I think the number you keep quoting of 75% is good general guidance for which set bonus to use. The damage curves between the two sets also look relatively flat where they cross (or flatter than they were), so really I think if you are within 5-10% of that point, you will not see too much difference between them.