So you are part right - given two different builders trying to copy code etc. would be a nightmare.
Opt 1: Replicate the new design content using VC into the main site - this wouldn’t be impossible but you might need to work a bit to get styling right and it is unlikely to be a perfect match.
Opt 2: Are you only using the new one as a landing page? If it is for that distinct purpose you could install it as a separate installation and redirect people. Again the issue is that it won;t be using your header/footer etc.