It seems you are talking about something different than I am.
What are the standards for the California Gray? How much does a hen weigh on average? How much does a rooster weigh on average?
Yes, I definitely seem to be talking about something different.
You are using weight as the sole criteria as to whether or not a bird qualifies as dual purpose or not. There are actually a range of factors - ratio of edible portion to live bird weight; feed efficiency in gaining weight (calmer breeds tend to gain more weight with less feed), and carcass quality - the type, texture, and distribution of edible portions.
The weight of an adult rooster isn't always relevant since a stag tends to be tough and strong flavored. One important point is the feed consumption to reach a certain weight before the cockerel is a tough stag - and how long that takes. The rate of return goes down dramatically in Leghorns between eight and twelve weeks, while a dual purpose bird gives a good rate of return up to between sixteen and twenty weeks. The other points regarding carcass quality and percentage of edible portion in a carcass have already been brought up here.
Which is why we are stuck looping on the topic.