Hi There,
Yes, Cornerstone was incorporated in PRO which in this Theme is called PRO Builder.
At this stage PRO Builder and the Cornerstone which you use with X are pretty much the same.
The main differences between the themes are
1- PRO Doe not offer demo content. We are working in a new solution to replace the demo content but it is not ready to be relesed but should be out soon but no ETA to be provided.
2- PRO offers the AMAZING Header and Footer Builders, which allow you to build extremely customizable headers and footers like no other Wordpress Theme.
The header and footer builder can seem a bit challenging at the beginning just like any new tool, but once you take your time to play a bit with it you will be amazed with the possibilities.
The only thing to have in mind is that differently from X Header the responsiveness is not automatic, you need to to hide the elements or show it based on screensize.
I reccomend you watching our video tutorials on our Knowledge Based and also there is a guy called Donald which made many tutorials on youtube about this.
Hope it helps