Thanks for writing in!
Cornerstone elements are based on Short-code, if you disable cornerstone then the content only show the short-code.
What is a shortcode?
A shortcode is a WordPress-specific code that lets you do nifty things with very little effort. Shortcodes can embed files or create objects that would normally require lots of complicated, ugly code in just one line.
We are really sorry but there is no other way to remove the shortcode other than manually remove it.
As you said you have switched to another theme, we are not sure what exactly the issue you have faced with our theme, if you could ask for a help we would love to help you any time.
Thanks for understanding.