The number of revisions should not cause the warning that you are getting in Cornerstone as that Wordpress feature will just keep track of the previous versions of the page.'
The code you are using seem to be alright. So kindly try the following:
Try to get the PHP memory limit of your site increased.
To do this, please edit your wp-config.php file and insert these lines:
define( 'WP_MEMORY_LIMIT', '256M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );
You can add it before the line
/*That's all, stop editing! Happy Blogging. */
Here is a details article about the PHP Memory Limit that is in our Knowledge Base:
In case the issue persists, please try to get in touch with your hosting provider and confirm to them that your PHP memory limit is increased.
If you are still having an issue, please provide us with the admin details of your site in a Secure Note so that we can check this further.