Quite a confusing statement. Let me reword it:
VEXCode was designed to be a direct upgrade from VCS, so don’t use VCS as updates for VCS are no longer being supported.
PROS is also another popular C++ programming platform, but learning it takes a lot of time to figure out. Also, as an addition, I would prefer doing VEXCode first, then consider PROS if you feel like you have learned the gist of C++ and how it operates.
RobotMesh doesn’t seem like a popular choice, not for any reason in particular but due to it’s lack of advertising and community-ran assistance (such as in competition). If someone uses RobotMesh, the API’s are quite confusing, especially for those who want to code using python. That is why, although they have a good language and system, I would not recommend as the chance of someone in competition to use RobotMesh are unlikely.
I want to emphasize that PROS is a very heavy software. If you are a beginner and immediately start out with PROS, you may learn PROS but you may learn PROS in a manner that is not optimal. It will be better to first learn VEXCode, and maybe take a Computer Science High School course to understand how brackets, functions, syntax, and file management works before exposing yourself to something difficult to learn. By immediately jumping to PROS on your own, you will be basically putting yourself on the frontlines with no tools, weapons, or experience.