They generally come straight run. Females can certainly grow as large as the males, they just take an extra week or 2 to get there. None of the females I have ever raised were tiny. They were in the same weight range as their brothers at processing time.
It isn't a dumb question. The original ones were a result of a Cornish crossed with a white Rock. That was decades ago. These days they are the result of highly specialized and selective breeding program, involving a 4 way cross.