Support has answered this question many many times if you looked. They know that VC is not updated to its most current version, I think iuts because they are trying to push Cornerstone rather than ppl using VC
Here is a link to someone asking about why they cant update VC to its most current version
Support said
Unfortunately, the original version of the VIsual Composer is not compatible with our theme. To make the VC compatible we did change some aspects of the code.
The only thing I can think of is that you do the customization on our version of the plugin. But you need to keep the customization and do it again on each VC release from our side.
Needless to say that Cornerstone is the builder which we encourage to use.