In any professional project I've ever worked on, the compiler version has been strictly controlled. The entire team must use the same version of Visual Studio, or Xcode, or the JDK, or the Android build tools or whatever. You don't just let your developers upgrade whenever they want. Upgrading the build tools is an involved process that must be coordinated with the release cycle. All new warnings need to be fixed, all CI nodes need to be upgraded at once, scripts and metadata need fixes to work with the new tools, etc.
You are only approaching this issue from the perspective of open source software. That is not most software. The parent is correct: the compiler version is a dependency of your project and, in any serious development team, should be fixed for the whole team.