Yes, that is correct. The Blog is powered by the index PHP template and could not be edited Cornerstone nor anywhere else in WP Admin.
To your question:
Since it could not be edited, regretfully, this is not possible. This would require template customization which is outside the scope of our support.
What you can do instead is use Essential Grid or The Grid plugin to display your posts inside a Cornerstone built page. Both plugins come bundled in Pro.