I would make that trade. There is no way to predict how someone will do over the course of the season in ML baseball without a decent track record, but the odds are that both Garza and McCarthy will be effective.
The White Sox are a much better hitting team, so I would anticipate more wins for McCarthy, more K's for Garza and other stats about equal.
However, barring injuries, there is a 95% chance that Garza will be starting all next year.
I think there is only a 50% chance that McCarthy will start next year. Their only potential free agent is Beurhle, and as their only lefty I would imagine there will be a strong effort to resign him. That means they must either not resign him or trade Garcia, Contreras, Vasquez, or Garland. I view that as 50-50.