Would you mind providing a performance report about this? Cornerstone builder will only loads up when you use its builder and it's only logical to use some resources since you're building your site and page, and it may load longer depending on the amount of the content you're building.
But if you're referring to the live page (not in the builder), then yes 6 seconds is long enough, but I don't see any connection with cornerstone since it's a live page where builder isn't loaded. The only resources being pulled from cornerstone are scripts required for elements to work and CSS for design.
And I don't see this issue on other sites either.